#1876 - Substrings of Size Three with Distinct Characters

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String Hash Table Counting Sliding Window

Problem Description

A string is good if there are no repeated characters.

Given a string s, return the number of good substrings of length three in s.

Note that if there are multiple occurrences of the same substring, every occurrence should be counted.

A substring is a contiguous sequence of characters in a string.

Solution

/**
 * @param {string} s
 * @return {number}
 */
var countGoodSubstrings = function(s) {
  if (s.length < 3) return 0;

  let result = 0;
  const charCount = new Map();

  for (let i = 0; i < 3; i++) {
    charCount.set(s[i], (charCount.get(s[i]) || 0) + 1);
  }
  if (charCount.size === 3) result++;

  for (let i = 3; i < s.length; i++) {
    const oldChar = s[i - 3];
    charCount.set(oldChar, charCount.get(oldChar) - 1);
    if (charCount.get(oldChar) === 0) charCount.delete(oldChar);

    charCount.set(s[i], (charCount.get(s[i]) || 0) + 1);
    if (charCount.size === 3) result++;
  }

  return result;
};