permutation_in_string.cpp

class Solution {
private:
    bool checker(int a[26], int b[26]){
        for(int i=0; i<26; i++){
            if(a[i]!=b[i]){
                return 0;
            }
        }
        return 1;
    }
public:
    bool checkInclusion(string s1, string s2) {
        int count1[26] = {0};

        for(int i=0; i<s1.length(); i++){
            int index = s1[i] - 'a';
            count1[index]++;
        }


        int i = 0;
        int windowSize = s1.length();
        int count2[26]={0};

        while(i < windowSize && i < s2.length()){
            int index = s2[i] - 'a';
            count2[index]++;

            i++;
        }
        if(checker(count1, count2))
           return 1;

        while(i<s2.length()){
            char newChar = s2[i];
            int index = newChar-'a';
            count2[index]++;

            char oldChar = s2[i-windowSize];
            index = oldChar - 'a';
            count2[index]--;
            i++;

        if(checker(count1, count2))
           return 1;

        }

        return 0;
    }
};