LeetCode-in-All

438. Find All Anagrams in a String

Medium

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.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

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:

Solution

#include <vector>
#include <string>
using namespace std;

class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        vector<int> map(26, 0);
        for (char c : p) {
            map[c - 'a']++;
        }

        vector<int> res;
        int i = 0, j = 0;

        while (i < s.length()) {
            int idx = s[i] - 'a';
            // Add the new character
            map[idx]--;

            // If the length is greater than window's length, pop the left character in the window
            if (i >= p.length()) {
                map[s[j++] - 'a']++;
            }

            bool finish = true;
            for (int k = 0; k < 26; k++) {
                // If it is not an anagram of string p
                if (map[k] != 0) {
                    finish = false;
                    break;
                }
            }

            if (i >= p.length() - 1 && finish) {
                res.push_back(j);
            }

            i++;
        }

        return res;
    }
};