387. First Unique Character in a String

Problem:

Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Analysis:
The idea is two pass. First pass count currency in map. Second path, find the first count == 1's char in map.

Solution:

class Solution {
    public int firstUniqChar(String s) {
        if (s == null || s.length() == 0)
   return -1;
  int res = 0;
  Set<Character> checkSet = new HashSet<>();
  Set<Character> dupSet = new HashSet<>();
  for (char c: s.toCharArray()) {
   if (!checkSet.add(c)) {
    dupSet.add(c);
   }
  }

  for (int i = 0; i < s.length(); i++) {
   if (!dupSet.contains(s.charAt(i)))
    return i;
  }
  return -1;
    }
}