387. First Unique Character in a String

Problem

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

  Example 1:

Input: s = "leetcode"
Output: 0

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

  Constraints:

• 1 <= s.length <= 10^5

• s consists of only lowercase English letters.

Solution (Java)

class Solution {
    public int firstUniqChar(String s) {
        int ans = Integer.MAX_VALUE;
        for (char i = 'a'; i <= 'z'; i++) {
            int ind = s.indexOf(i);
            if (ind != -1 && ind == s.lastIndexOf(i)) {
                ans = Math.min(ans, ind);
            }
        }
        if (ans == Integer.MAX_VALUE) {
            return -1;
        }
        return ans;
    }
}

Solution (Javascript)

/**
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function(s) {
  if (s.length === 0) return -1;

    for( let i = 0; i < s.length; i++) {
       const letter = s[i]

       if(s.indexOf(letter) === s.lastIndexOf(letter)) return i
   }

   return -1
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).