Basic example
Input
s = 'cbaebabacd', p = 'abc'
Output
[0, 6]
Substrings 'cba' at index 0 and 'bac' at index 6 are anagrams of 'abc'.
Full lesson preview
Find all anagrams of a pattern in a string
Return start indices of all anagrams of a pattern inside a string using a sliding window.
Python practice14 minTwo Pointers & Sliding WindowIntermediateLast updated March 26, 2026
Problem statement
Given a string s and a pattern p, find all start indices of p's anagrams in s. An anagram is a rearrangement of letters. Return a list of starting indices in ascending order. If none exist, return an empty list. Assume s and p contain only lowercase English letters.
Task
Use a fixed-size sliding window and character frequency comparison to locate all anagram starting indices in linear time.
Examples
Input format
Two strings s and p.
Output format
A list of integers representing start indices (e.g. [0, 6]).
Constraints
0 <= len(s), len(p) <= 10^5. Only lowercase English letters. Expected time O(n).
Samples
Sample 1
Input
s = 'abab', p = 'ab'
Output
[0, 1, 2]
All substrings starting at 0,1,2 are anagrams of 'ab'.