Li Kou 1358 -- number of substrings containing all three characters (double pointer)

Double finger needling

Find all that appears abc String , In the future, each additional person will have one more answer ;

Looking for all that appears abc String process with double finger needle method to avoid O(N^2) Overtime , Specific to the code is the right pointer plus , Left pointer minus

Complexity O(N)

class Solution {
    
public:
    int numberOfSubstrings(string s) {
    
        vector<int> cnt(3, 0);
        int n = s.size();
        int left = -1, right = 0;
        int ans = 0;
        while(right < n) {
    
            cnt[s[right] - 'a']++;
            if(cnt[0] && cnt[1] && cnt[2]) {
    
               ans += n - right;
               left++;
               cnt[s[left] - 'a']--;
            }
            else {
    
                right++;
            }
        }
        return ans;
    }
};