1358. Number of Substrings Containing All Three Characters

1358. Number of Substrings Containing All Three Characters (Medium)

Given a string s consisting only of characters a, b and c.

Return the number of substrings containing at least one occurrence of all these characters a, b and c.

 

Example 1:

Input: s = "abcabc"
Output: 10
Explanation: The substrings containing at least one occurrence of the characters a, b and c are "abc", "abca", "abcab", "abcabc", "bca", "bcab", "bcabc", "cab", "cabc" and "abc" (again). 

Example 2:

Input: s = "aaacb"
Output: 3
Explanation: The substrings containing at least one occurrence of the characters a, b and c are "aaacb", "aacb" and "acb". 

Example 3:

Input: s = "abc"
Output: 1

 

Constraints:

• 3 <= s.length <= 5 x 10^4
• s only consists of a, b or c characters.

Related Topics:
String

Solution 1. Sliding Window

// OJ: https://leetcode.com/problems/number-of-substrings-containing-all-three-characters/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
    int cnt[3] = {0};
    bool valid() {
        for (int n : cnt) 
            if (!n) return false;
        return true;
    }
public:
    int numberOfSubstrings(string s) {
        int L = 0, R = 0, N = s.size(), ans = 0;
        while (R < N) { 
            if (!valid()) cnt[s[R++] - 'a']++;
            while (valid()) {
                ans += N - R + 1;
                cnt[s[L++] - 'a']--;
            }
        }
        return ans;
    }
};