Leetcode - Find All Anagrams in a String Solution

Given two strings s and p, return an array of all the start indices of p's anagrams in s. You may return the answer in any order.

Example 1:

Input: s = "cbaebabacd", p = "abc"
Output: [0,6]
Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".

Example 2:

Input: s = "abab", p = "ab"
Output: [0,1,2]
Explanation:
The substring with start index = 0 is "ab", which is an anagram of "ab".
The substring with start index = 1 is "ba", which is an anagram of "ab".
The substring with start index = 2 is "ab", which is an anagram of "ab".

Constraints:

• 1 <= s.length, p.length <= 3 * 104
• s and p consist of lowercase English letters.

Solution in Python

class Solution:
    def findAnagrams(self, s: str, p: str) -> List[int]:
        start = 0
        stop = len(p)-1
        found = []
        count_s = Counter(s[start:stop])
        count_p = Counter(p) 
        for i in range(stop,len(s)):
            first_letter = s[i-stop]
            last_letter = s[i]
            count_s[last_letter]+=1
            if count_s == count_p:
                found.append(i-stop)
            if count_s[first_letter] == 1:
                del count_s[first_letter]
            else:
                count_s[first_letter] -= 1
        return found