Formatted question description: https://leetcode.ca/all/1358.html

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 ab 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 ab 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 characters.

Related Topics:
String

Solution 1. Sliding Window

// OJ: https://leetcode.com/problems/number-of-substrings-containing-all-three-characters/

// 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;
    }
};

Java

  • class Solution {
        public int numberOfSubstrings(String s) {
            int substrings = 0;
            int[] counts = new int[3];
            int length = s.length();
            int lettersCount = 0;
            int start = 0, end = 0;
            while (end < length) {
                char c = s.charAt(end);
                counts[c - 'a']++;
                if (counts[c - 'a'] == 1)
                    lettersCount++;
                while (lettersCount == 3) {
                    substrings += length - end;
                    char prevC = s.charAt(start);
                    start++;
                    counts[prevC - 'a']--;
                    if (counts[prevC - 'a'] == 0)
                        lettersCount--;
                }
                end++;
            }
            return substrings;
        }
    }
    
  • // OJ: https://leetcode.com/problems/number-of-substrings-containing-all-three-characters/
    // 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;
        }
    };
    
  • print("Todo!")
    

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