Basic example
Input
s = "cbaebabacd", p = "abc"
Output
[0, 6]
The substring at index 0 is "cba" which is an anagram of "abc". The substring at index 6 is "bac" which is also an anagram.
Full lesson preview
Find all start indices of pattern anagrams
Return all starting indices of p's anagrams in s using sliding window and frequency counting.
Python practice15 minStrings – Sliding Window & FrequencyIntermediateLast updated March 25, 2026
Problem statement
Given two strings s and p, return a list of all start indices of p's anagrams in s. An anagram is a permutation of the pattern. The order of output indices does not matter. Use a sliding window and frequency counting to achieve O(n) time complexity.
Task
Use a fixed-size sliding window plus frequency counts to detect anagrams of a pattern within a text string.
Examples
Input format
Two string arguments: s (text) and p (pattern). Example: find_anagrams("cbaebabacd", "abc")
Output format
A list of integers representing starting indices. Example: [0, 6]
Constraints
0 <= len(s), len(p) <= 10^5. Only ASCII lowercase letters assumed for typical inputs, but solution should work with general characters.
Samples
Sample 1
Input
s = "abab", p = "ab"
Output
[0, 1, 2]
All substrings "ab","ba","ab" are anagrams of "ab" at indices 0,1,2.