Number of Substrings Containing All Three Characters

Description

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.

Solution(javascript)

/** Sliding Window?
 * @param {string} s
 * @return {number}
 */
const numberOfSubstrings = function (s) {
  let result = 0
  const isValid = map => map.a >= 1 && map.b >= 1 && map.c >= 1
  const map = {}
  let front = 0
  for (let i = 0; i < s.length; i++) {
    map[s[i]] = (map[s[i]] || 0) + 1
    if (isValid(map)) {
      result += s.length - i
      map[s[front++]] -= 1
      while (isValid(map)) {
        result += s.length - i
        map[s[front++]] -= 1
      }
    }
  }
  return result
}