387.first-unique-character-in-a-string.java

import java.util.HashMap;

/*
 * @lc app=leetcode id=387 lang=java
 *
 * [387] First Unique Character in a String
 */

// @lc code=start
class Solution {
    public int firstUniqChar(String s) {
        HashMap<Character, Integer> letters = new HashMap<>();

        for (int i = 0; i < s.length(); i++) {
            letters.put(s.charAt(i), letters.getOrDefault(s.charAt(i), 0) + 1);
        }

        for (int i = 0; i < s.length(); i++) {
            if (letters.get(s.charAt(i)) == 1) {
                return i;
            }
        }
        return -1;
    }
}
// @lc code=end