Longest Nice Substring LeetCode solution in Java

1
class Solution {
2
  public String longestNiceSubstring(String s) {
3
    String result = "";
4
    // take first index, go from 0 to length-1 of the string
5
    for (int i = 0; i < s.length(); i++) {
6
      // take second index, this should go up to the length of the string <=
7
      for (int j = i + 1; j <= s.length(); j++) {
8
        // get the substring for the index range from i to j
9
        String temp = s.substring(i, j);
10
        // if length of the substring should be greater than 1
11
        // if the length should be greater that the previous computed result
12
        // if the substring is valid Nice String
13
        // then update the result with the current substring from range i and j
14
        if (temp.length() > 1 && result.length() < temp.length() && checkNice(temp)) result = temp;
15
      }
16
    }
17
    return result;
18
  }
19

20
  // validate Nice String check
21
  public boolean checkNice(String temp) {
22
    // add substring to the set
23
    Set<Character> s = new HashSet<>();
24
    for (char ch : temp.toCharArray()) s.add(ch);
25

26
    // return false If you do not find both lower case and upper case in the sub string
27
    // for e.g 'aAa' substring added to set will have both a and A in the substring which is valid
28
    // 'azaA' substring will fail for 'z'
29
    // 'aaaaaaaa' will return "" as result
30
    // make sure that the substring contains both lower and upper case
31
    for (char ch : s)
32
      if (s.contains(Character.toUpperCase(ch)) != s.contains(Character.toLowerCase(ch)))
33
        return false;
34
    return true;
35
  }
36
}