First Unique Character in a String

Java

public class Solution {
    /**
     * @param str: str: the given string
     * @return: char: the first unique character in a given string
     */
    public char firstUniqChar(String str) {
        // Write your code here
        HashMap<Character, Integer> map = new HashMap<>();
        Queue<Character> queue = new LinkedList<>();
        
        for (char c : str.toCharArray()) {
            if (map.containsKey(c)) {
                map.put(c, map.get(c) + 1);
            } else {
                map.put(c, 1);
                queue.offer(c);
            }
        }
        while (!queue.isEmpty() && map.get(queue.peek()) != 1) {
            queue.poll();
        }
        return queue.peek();
    }
}