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Practice › LeetCode › LeetCode 39xx ›

LeetCode 3934 - Smallest Unique Subarray

LeetCode Problem 3934 Difficulty: 🔴 Hard Topics: Array, Hash Table, Binary Search, Rolling Hash, Suffix Array, Hash Function Solution Problem Understanding The problem asks us to find the smallest possible length of a contiguous subarray such that there exists at least one subarray of that length that appears exactly once in the entire array. In other words, for a fixed length L , we look at every subarray of size...
leetcode Hard array hash-table binary-search rolling-hash suffix-array hash-function Jun 10, 2026
Practice › LeetCode › LeetCode 37xx ›

LeetCode 3735 - Lexicographically Smallest String After Reverse II

LeetCode Problem 3735 Difficulty: 🔴 Hard Topics: String, Binary Search, Rolling Hash, Suffix Array, Hash Function Solution Problem Understanding The problem is asking us to manipulate a string s of length n in order to produce the lexicographically smallest possible string after exactly one operation. The operation allows you to choose an integer k between 1 and n and either reverse the first k characters or reverse the last k...
leetcode Hard string binary-search rolling-hash suffix-array hash-function Jun 10, 2026
Practice › LeetCode › LeetCode 35xx ›

LeetCode 3529 - Count Cells in Overlapping Horizontal and Vertical Substrings

LeetCode Problem 3529 Difficulty: 🟡 Medium Topics: Array, String, Rolling Hash, String Matching, Matrix, Hash Function Solution Problem Understanding We are given a character matrix and a pattern string. The key observation is that the problem defines two unusual traversal orders: A horizontal traversal reads the matrix row by row, from left to right. When a row ends, reading continues at the beginning of the next row. A vertical traversal...
leetcode Medium array string rolling-hash string-matching matrix hash-function May 30, 2026
Practice › LeetCode › LeetCode 31xx ›

LeetCode 3135 - Equalize Strings by Adding or Removing Characters at Ends

LeetCode Problem 3135 Difficulty: 🟡 Medium Topics: String, Binary Search, Dynamic Programming, Sliding Window, Hash Function Solution Problem Understanding The problem gives us two strings, initial and target . We want to transform initial into target using the minimum number of operations. In a single operation, we may either: Add one character to the beginning of the string Add one character to the end of the string Remove one character...
leetcode Medium string binary-search dynamic-programming sliding-window hash-function May 30, 2026
Practice › LeetCode › LeetCode 19xx ›

LeetCode 1960 - Maximum Product of the Length of Two Palindromic Substrings

LeetCode Problem 1960 Difficulty: 🔴 Hard Topics: Two Pointers, String, Rolling Hash, Hash Function Solution LeetCode 1960 - Maximum Product of the Length of Two Palindromic Substrings Problem Understanding The problem asks us to find two non-overlapping odd-length palindromic substrings whose length product is as large as possible. We are given a string s of length up to 10^5 . We must choose two palindromic substrings: The first occupies indices...
leetcode Hard two-pointers string rolling-hash hash-function May 30, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3031 - Minimum Time to Revert Word to Initial State II

LeetCode Problem 3031 Difficulty: 🔴 Hard Topics: String, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem requires simulating a repetitive transformation on a string word where, at each second, the first k characters are removed, and then any k characters are appended to the end. The key challenge is to determine the minimum number of seconds required for the string to return exactly to its initial state....
leetcode Hard string rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3042 - Count Prefix and Suffix Pairs I

LeetCode Problem 3042 Difficulty: 🟢 Easy Topics: Array, String, Trie, Rolling Hash, String Matching, Hash Function Solution LeetCode 3042 - Count Prefix and Suffix Pairs I Problem Understanding The problem gives us an array of strings called words . For every pair of indices (i, j) where i < j , we must determine whether words[i] is both a prefix and a suffix of words[j] . A string is a...
leetcode Easy array string trie rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 32xx ›

LeetCode 3292 - Minimum Number of Valid Strings to Form Target II

LeetCode Problem 3292 Difficulty: 🔴 Hard Topics: Array, String, Binary Search, Dynamic Programming, Greedy, Segment Tree, Rolling Hash, String Matching, Hash Function Solution LeetCode 3292 - Minimum Number of Valid Strings to Form Target II Problem Understanding We are given a collection of strings words and a target string target . A string is considered valid if it is a prefix of at least one word in words . This...
leetcode Hard array string binary-search dynamic-programming greedy segment-tree rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3006 - Find Beautiful Indices in the Given Array I

LeetCode Problem 3006 Difficulty: 🟡 Medium Topics: Two Pointers, String, Binary Search, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem gives us a string s and two smaller strings, a and b . We need to find every index i where substring a appears in s , but only if there exists at least one occurrence of substring b close enough to it. More formally, an index...
leetcode Medium two-pointers string binary-search rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 24xx ›

LeetCode 2430 - Maximum Deletions on a String

LeetCode Problem 2430 Difficulty: 🔴 Hard Topics: String, Dynamic Programming, Rolling Hash, String Matching, Hash Function Solution Maximum Deletions on a String Problem Understanding The problem gives us a string s consisting only of lowercase English letters. We want to completely delete the string using the maximum possible number of operations. In a single operation, we have two possible actions: Delete the entire remaining string immediately. Delete only the first...
leetcode Hard string dynamic-programming rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 22xx ›

LeetCode 2223 - Sum of Scores of Built Strings

LeetCode Problem 2223 Difficulty: 🔴 Hard Topics: String, Binary Search, Rolling Hash, Suffix Array, String Matching, Hash Function Solution Problem Understanding The problem gives us a final string s and describes a process where the string is built by repeatedly prepending characters to the front. This means that every intermediate string si is actually a suffix of the final string s . For example, if: s = "abaca" Then: s1...
leetcode Hard string binary-search rolling-hash suffix-array string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 33xx ›

LeetCode 3327 - Check if DFS Strings Are Palindromes

LeetCode Problem 3327 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Tree, Depth-First Search, Hash Function Solution LeetCode 3327 - Check if DFS Strings Are Palindromes Problem Understanding We are given a rooted tree with n nodes. Node 0 is the root, and the parent-child relationships are described by the parent array. Each node i also has an associated character s[i] . For any node x , a DFS traversal...
leetcode Hard array hash-table string tree depth-first-search hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3023 - Find Pattern in Infinite Stream I

LeetCode Problem 3023 Difficulty: 🟡 Medium Topics: Array, Sliding Window, Rolling Hash, String Matching, Interactive, Hash Function Solution Problem Understanding The problem asks us to detect the first occurrence of a given binary pattern within an infinite stream of bits. We are given an object stream that allows us to read one bit at a time using the next() function. Our task is to return the 0-based index in the...
leetcode Medium array sliding-window rolling-hash string-matching interactive hash-function May 29, 2026
Practice › LeetCode › LeetCode 22xx ›

LeetCode 2261 - K Divisible Elements Subarrays

LeetCode Problem 2261 Difficulty: 🟡 Medium Topics: Array, Hash Table, Trie, Rolling Hash, Hash Function, Enumeration Solution Problem Understanding This problem requires counting the number of distinct subarrays of a given integer array nums that satisfy a specific constraint: each subarray can contain at most k elements divisible by p . A subarray is a contiguous slice of the array, and "distinct" means either differing in length or differing in...
leetcode Medium array hash-table trie rolling-hash hash-function enumeration May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3036 - Number of Subarrays That Match a Pattern II

LeetCode Problem 3036 Difficulty: 🔴 Hard Topics: Array, Rolling Hash, String Matching, Hash Function Solution This guide will be very long, likely exceeding a single message cleanly while still maintaining the level of detail and formatting quality you requested for a reference document. I can provide the complete guide in full , including: Problem Understanding Approaches (Brute Force + Optimal KMP) Algorithm Walkthrough Python Solution Go Solution Worked Examples (step-by-step...
leetcode Hard array rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3008 - Find Beautiful Indices in the Given Array II

LeetCode Problem 3008 Difficulty: 🔴 Hard Topics: Two Pointers, String, Binary Search, Rolling Hash, String Matching, Hash Function Solution LeetCode 3008 - Find Beautiful Indices in the Given Array II Problem Understanding This problem asks us to find every starting index where the substring a appears inside the string s , subject to an additional proximity condition involving another substring b . More specifically, an index i is considered beautiful...
leetcode Hard two-pointers string binary-search rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3034 - Number of Subarrays That Match a Pattern I

LeetCode Problem 3034 Difficulty: 🟡 Medium Topics: Array, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem asks us to count how many contiguous subarrays of nums match a given relationship pattern . Instead of comparing exact values, the pattern describes how adjacent numbers should relate to each other. Each value in pattern represents a comparison between two consecutive elements in a subarray: 1 means the next number...
leetcode Medium array rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 19xx ›

LeetCode 1923 - Longest Common Subpath

LeetCode Problem 1923 Difficulty: 🔴 Hard Topics: Array, Binary Search, Rolling Hash, Suffix Array, Hash Function Solution Problem Understanding The problem asks us to find the maximum length of a contiguous sequence of cities that appears in every friend's travel path. Each friend has a path represented as an array of city IDs. A subpath is simply a contiguous segment of that array. We need to determine the longest subpath...
leetcode Hard array binary-search rolling-hash suffix-array hash-function May 29, 2026
Practice › LeetCode › LeetCode 21xx ›

LeetCode 2156 - Find Substring With Given Hash Value

LeetCode Problem 2156 Difficulty: 🔴 Hard Topics: String, Sliding Window, Rolling Hash, Hash Function Solution Problem Understanding This problem asks us to find the earliest substring of length k whose polynomial rolling hash equals a given target value. The hash function is defined as: $$hash(s, p, m) = \left( \sum_{i=0}^{k-1} val(s[i]) \cdot p^i \right) \bmod m$$ where: val('a') = 1 val('b') = 2 ... val('z') = 26 For a substring...
leetcode Hard string sliding-window rolling-hash hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3029 - Minimum Time to Revert Word to Initial State I

LeetCode Problem 3029 Difficulty: 🟡 Medium Topics: String, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem gives us a string word and an integer k . Every second, we are forced to perform two operations in sequence: Remove the first k characters from the string. Append any k characters to the end of the string. The appended characters are completely under our control. They do not need...
leetcode Medium string rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3045 - Count Prefix and Suffix Pairs II

LeetCode Problem 3045 Difficulty: 🔴 Hard Topics: Array, String, Trie, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem asks us to count the number of ordered pairs (i, j) in a list of strings words such that i < j and words[i] is both a prefix and a suffix of words[j] . In other words, for a pair to be valid, the smaller-indexed string must appear at...
leetcode Hard array string trie rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 32xx ›

LeetCode 3291 - Minimum Number of Valid Strings to Form Target I

LeetCode Problem 3291 Difficulty: 🟡 Medium Topics: Array, String, Binary Search, Dynamic Programming, Greedy, Trie, Segment Tree, Rolling Hash, String Matching, Hash Function Solution Problem Understanding We are given a list of strings called words and another string called target . The task is to construct target by concatenating several smaller strings, where each smaller string must be a prefix of at least one word in words . A prefix...
leetcode Medium array string binary-search dynamic-programming greedy trie segment-tree rolling-hash string-matching hash-function May 29, 2026
Practice › LeetCode › LeetCode 21xx ›

LeetCode 2168 - Unique Substrings With Equal Digit Frequency

LeetCode Problem 2168 Difficulty: 🟡 Medium Topics: Hash Table, String, Rolling Hash, Counting, Hash Function Solution Problem Understanding The problem gives us a string s consisting only of digits from '0' to '9' . We must count how many distinct substrings satisfy a special condition: Every digit that appears in the substring must appear the same number of times. A substring is a contiguous portion of the string. The substring...
leetcode Medium hash-table string rolling-hash counting hash-function May 29, 2026
Practice › LeetCode › LeetCode 19xx ›

LeetCode 1948 - Delete Duplicate Folders in System

LeetCode Problem 1948 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Trie, Hash Function Solution Problem Understanding The problem gives a hierarchical file system represented as a list of absolute paths, where each path is an array of folder names from the root to a leaf folder. From these paths, we must reconstruct the implicit tree structure of folders, where each node represents a folder and edges represent parent-child relationships....
leetcode Hard array hash-table string trie hash-function May 29, 2026
Practice › LeetCode › LeetCode 30xx ›

LeetCode 3037 - Find Pattern in Infinite Stream II

LeetCode Problem 3037 Difficulty: 🔴 Hard Topics: Array, Sliding Window, Rolling Hash, String Matching, Interactive, Hash Function Solution Problem Understanding The problem requires us to detect the first occurrence of a binary pattern within a theoretically infinite stream of bits. The stream is accessed sequentially using the next() method, which returns one bit at a time. Our task is to determine the index in the stream where the given pattern...
leetcode Hard array sliding-window rolling-hash string-matching interactive hash-function May 29, 2026
Practice › LeetCode › LeetCode 05xx ›

LeetCode 572 - Subtree of Another Tree

LeetCode Problem 572 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, String Matching, Binary Tree, Hash Function Solution LeetCode 572 - Subtree of Another Tree Problem Understanding This problem asks us to determine whether one binary tree appears as an exact subtree inside another binary tree. We are given two binary trees: root , the main tree subRoot , the candidate subtree We must return true if there exists some node...
leetcode Easy tree depth-first-search string-matching binary-tree hash-function May 28, 2026
Practice › LeetCode › LeetCode 05xx ›

LeetCode 535 - Encode and Decode TinyURL

LeetCode Problem 535 Difficulty: 🟡 Medium Topics: Hash Table, String, Design, Hash Function Solution Problem Understanding The problem asks us to implement a URL shortening service, similar to TinyURL. Given a long URL, our system should generate a short, unique URL that maps back to the original URL. When the short URL is accessed, the system should return the original long URL. Essentially, we need a reversible mapping between long...
leetcode Medium hash-table string design hash-function May 28, 2026
Practice › LeetCode › LeetCode 15xx ›

LeetCode 1554 - Strings Differ by One Character

LeetCode Problem 1554 Difficulty: 🟡 Medium Topics: Hash Table, String, Rolling Hash, Hash Function Solution Problem Understanding This problem gives us an array of unique strings called dict , where every string has the same length. We must determine whether there exists at least one pair of strings that differ by exactly one character at the same position. In other words, we are looking for two strings where: Their lengths...
leetcode Medium hash-table string rolling-hash hash-function May 28, 2026
Practice › LeetCode › LeetCode 07xx ›

LeetCode 711 - Number of Distinct Islands II

LeetCode Problem 711 Difficulty: 🔴 Hard Topics: Array, Hash Table, Depth-First Search, Breadth-First Search, Union-Find, Sorting, Matrix, Hash Function Solution Problem Understanding In this problem, we are given a binary matrix where each cell contains either 0 or 1 . A value of 1 represents land, while 0 represents water. An island is formed by connecting adjacent land cells in the four cardinal directions: up, down, left, and right. The...
leetcode Hard array hash-table depth-first-search breadth-first-search union-find sorting matrix hash-function May 28, 2026
Practice › LeetCode › LeetCode 03xx ›

LeetCode 336 - Palindrome Pairs

LeetCode Problem 336 Difficulty: 🔴 Hard Topics: Array, Hash Table, String, Trie, Hash Function Solution Problem Understanding The problem gives us a list of unique strings called words . We must find every ordered pair of indices (i, j) such that: i != j concatenating words[i] + words[j] forms a palindrome A palindrome is a string that reads the same forward and backward. The important detail is that the pairs...
leetcode Hard array hash-table string trie hash-function May 28, 2026
Practice › LeetCode › LeetCode 16xx ›

LeetCode 1698 - Number of Distinct Substrings in a String

LeetCode Problem 1698 Difficulty: 🟡 Medium Topics: String, Trie, Rolling Hash, Suffix Array, Hash Function Solution Problem Understanding The problem asks for the total number of distinct substrings of a given string s . A substring is any contiguous sequence of characters from the string, including single-character substrings and the string itself. The output is an integer representing how many unique substrings can be formed from s . For example,...
leetcode Medium string trie rolling-hash suffix-array hash-function May 28, 2026
Practice › LeetCode › LeetCode 07xx ›

LeetCode 706 - Design HashMap

LeetCode Problem 706 Difficulty: 🟢 Easy Topics: Array, Hash Table, Linked List, Design, Hash Function Solution Problem Understanding The problem requires us to implement a HashMap from scratch without using any built-in hash table libraries. In other words, we need to create a data structure that can store key-value pairs, allow efficient insertion, retrieval, and deletion of values based on their keys. The input operations consist of put , get...
leetcode Easy array hash-table linked-list design hash-function May 28, 2026
Practice › LeetCode › LeetCode 10xx ›

LeetCode 1062 - Longest Repeating Substring

LeetCode Problem 1062 Difficulty: 🟡 Medium Topics: String, Binary Search, Dynamic Programming, Rolling Hash, Suffix Array, Hash Function Solution Problem Understanding The problem asks us to find the length of the longest substring that appears at least twice in a given string s . A substring is a contiguous sequence of characters inside a string. The repeated substrings may overlap with each other, which is an important detail. For example,...
leetcode Medium string binary-search dynamic-programming rolling-hash suffix-array hash-function May 28, 2026
Practice › LeetCode › LeetCode 07xx ›

LeetCode 705 - Design HashSet

LeetCode Problem 705 Difficulty: 🟢 Easy Topics: Array, Hash Table, Linked List, Design, Hash Function Solution Problem Understanding The problem asks us to design our own HashSet implementation without using any built in hash table libraries such as Python's set or Go's built in map type as the primary solution idea. A HashSet is a data structure that stores unique values. It supports three operations: add(key) , insert a value...
leetcode Easy array hash-table linked-list design hash-function May 28, 2026
Practice › LeetCode › LeetCode 14xx ›

LeetCode 1461 - Check If a String Contains All Binary Codes of Size K

LeetCode Problem 1461 Difficulty: 🟡 Medium Topics: Hash Table, String, Bit Manipulation, Rolling Hash, Hash Function Solution Problem Understanding The problem gives us a binary string s and an integer k . A binary string contains only the characters '0' and '1' . We must determine whether every possible binary code of length k appears somewhere inside s as a substring. A binary code of length k is simply any...
leetcode Medium hash-table string bit-manipulation rolling-hash hash-function May 28, 2026
Practice › LeetCode › LeetCode 10xx ›

LeetCode 1044 - Longest Duplicate Substring

LeetCode Problem 1044 Difficulty: 🔴 Hard Topics: String, Binary Search, Sliding Window, Rolling Hash, Suffix Array, Hash Function Solution Here is the complete, detailed technical solution guide for LeetCode 1044 - Longest Duplicate Substring, following your formatting rules exactly. Problem Understanding The problem asks us to find the longest duplicated substring in a given string s . A duplicated substring is a contiguous sequence of characters that appears at least...
leetcode Hard string binary-search sliding-window rolling-hash suffix-array hash-function May 28, 2026
Practice › LeetCode › LeetCode 01xx ›

LeetCode 187 - Repeated DNA Sequences

LeetCode Problem 187 Difficulty: 🟡 Medium Topics: Hash Table, String, Bit Manipulation, Sliding Window, Rolling Hash, Hash Function Solution Problem Understanding This problem asks us to find all repeated DNA subsequences of a fixed length, specifically length 10 , inside a given DNA string. The input is a string s , where each character represents a DNA nucleotide. The string contains only four possible characters: 'A' 'C' 'G' 'T' We...
leetcode Medium hash-table string bit-manipulation sliding-window rolling-hash hash-function May 28, 2026
Practice › LeetCode › LeetCode 02xx ›

LeetCode 214 - Shortest Palindrome

LeetCode Problem 214 Difficulty: 🔴 Hard Topics: String, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem gives a string s and asks us to create the shortest possible palindrome by adding characters only at the beginning of the string. A palindrome is a string that reads the same forward and backward. The key restriction is that we are not allowed to insert characters in the middle or...
leetcode Hard string rolling-hash string-matching hash-function May 28, 2026
Practice › LeetCode › LeetCode 06xx ›

LeetCode 694 - Number of Distinct Islands

LeetCode Problem 694 Difficulty: 🟡 Medium Topics: Array, Hash Table, Depth-First Search, Breadth-First Search, Union-Find, Sorting, Matrix, Hash Function Solution Problem Understanding The problem gives us a binary matrix called grid , where each cell contains either 0 or 1 . A value of 1 represents land, and a value of 0 represents water. An island is formed by connecting adjacent land cells in the four cardinal directions: up, down,...
leetcode Medium array hash-table depth-first-search breadth-first-search union-find sorting matrix hash-function May 28, 2026
Practice › LeetCode › LeetCode 11xx ›

LeetCode 1147 - Longest Chunked Palindrome Decomposition

LeetCode Problem 1147 Difficulty: 🔴 Hard Topics: Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function Solution Problem Understanding The problem asks us to decompose a given string text into the largest possible number of contiguous substrings such that the sequence of substrings forms a palindromic pattern. Specifically, the first substring must equal the last substring, the second substring must equal the second-to-last substring, and so on. The goal...
leetcode Hard two-pointers string dynamic-programming greedy rolling-hash hash-function May 28, 2026
Practice › LeetCode › LeetCode 07xx ›

LeetCode 718 - Maximum Length of Repeated Subarray

LeetCode Problem 718 Difficulty: 🟡 Medium Topics: Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function Solution Problem Understanding The problem asks us to find the longest contiguous subarray that appears in both input arrays. A subarray is different from a subsequence because the elements must remain adjacent. This distinction is extremely important because many similar problems allow gaps, but this one does not. We are given two...
leetcode Medium array binary-search dynamic-programming sliding-window rolling-hash hash-function May 28, 2026
Practice › LeetCode › LeetCode 13xx ›

LeetCode 1392 - Longest Happy Prefix

LeetCode Problem 1392 Difficulty: 🔴 Hard Topics: String, Rolling Hash, String Matching, Hash Function Solution Problem Understanding The problem asks us to find the longest substring that is both a prefix and a suffix of the given string s , while also ensuring that the substring is not equal to the entire string itself. A prefix is a substring that starts at index 0 , while a suffix is a...
leetcode Hard string rolling-hash string-matching hash-function May 28, 2026
Practice › LeetCode › LeetCode 13xx ›

LeetCode 1316 - Distinct Echo Substrings

LeetCode Problem 1316 Difficulty: 🔴 Hard Topics: String, Trie, Rolling Hash, Hash Function Solution Problem Understanding The problem asks us to find the number of distinct non-empty substrings of a given string text that can be expressed as the concatenation of some string with itself. In other words, we need to count all substrings of the form a + a , where a is any non-empty string. For example, "abcabc"...
leetcode Hard string trie rolling-hash hash-function May 28, 2026