0567-permutation-in-string.cpp

class Solution {
public:
    bool checkInclusion(string s1, string s2) {
        vector<int> cur(26), goal(26);
        for(char c : s1) goal[c - 'a']++;
        for(int i = 0; i < s2.size(); i++) {
            cur[s2[i] - 'a']++;
            if (i >= s1.size()) cur[s2[i - s1.size()] - 'a']--;
            if (goal == cur) return true;
        }
        return false;
    }
};