Sliding window on the learning road

Sliding window is mainly used to reduce the number of iterations , When knowing the required range of data , You can quickly traverse by adding and subtracting .

567. Permutation in String

class Solution {
public:
    bool checkInclusion(string s1, string s2) {
        int n=s1.size();
        int t=s2.size();
        vector<int>cnt1(26);
        vector<int>cnt2(26);
        if(t<n)
        return false;
        for(int i=0;i<n;i++)
        {
            cnt1[s1[i]-'a']++;
            cnt2[s2[i]-'a']++;
        }
        if(cnt1==cnt2)// Two vector The container can directly judge whether it is equal 
        return true;
        for(int i=n;i<t;i++)
        {
            cnt2[s2[i]-'a']++;
            cnt2[s2[i-n]-'a']--;// Apply sliding window algorithm 
            if(cnt1==cnt2)
            return true;
        }
        return false;
    }
};