#1763 - Longest Nice Substring

Easy • View on LeetCode • View on GitHub

String Hash Table Bit Manipulation Sliding Window Divide and Conquer

Problem Description

A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, "abABB" is nice because 'A' and 'a' appear, and 'B' and 'b' appear. However, "abA" is not because 'b' appears, but 'B' does not.

Given a string s, return the longest substring of s that is nice. If there are multiple, return the substring of the earliest occurrence. If there are none, return an empty string.

Solution

/**
 * @param {string} s
 * @return {string}
 */
var longestNiceSubstring = function(s) {
  let longest = '';

  for (let i = 0; i < s.length; i++) {
    for (let j = i; j < s.length; j++) {
      const substr = s.slice(i, j + 1);
      if (substr.length <= longest.length) continue;
      const chars = new Set(substr.toLowerCase().split(''));
      let isNice = true;
      for (const char of chars) {
        if (!substr.includes(char.toLowerCase()) || !substr.includes(char.toUpperCase())) {
          isNice = false;
          break;
        }
      }
      if (isNice) longest = substr;
    }
  }

  return longest;
};