1358. Number of Substrings Containing All Three Characters

Problem Statement

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.

Intuition

Approach:

As an when we get all occurences of a, b and c
We take all the sub-arrays  from that point till end
eg-
abc|abc
At index 2 we get all
So we take n-j
6-2=4 We get 4 sub arrays : abc, abca, abcab, abcabc
Like that

Video Links

Approach 1:

Sliding Window

C++

class Solution {
public:
    int numberOfSubstrings(string s) {
        unordered_map<char,int> mp;
        int ans=0, low=0, n=s.size();

        for(int high=0; high<s.size(); high++){
            mp[s[high]]++;

            while(mp['a'] and mp['b'] and mp['c']){
                ans += n-high;
                mp[s[low]]--;
                low++;
            }
        }

        return ans;
    }
};

Approach 2:

C++

Approach 3:

C++

Approach 4:

C++