题目：

题解：

class Solution {public int firstUniqChar(String s) {Map<Character, Integer> position = new HashMap<Character, Integer>();Queue<Pair> queue = new LinkedList<Pair>();int n = s.length();for (int i = 0; i < n; ++i) {char ch = s.charAt(i);if (!position.containsKey(ch)) {position.put(ch, i);queue.offer(new Pair(ch, i));} else {position.put(ch, -1);while (!queue.isEmpty() && position.get(queue.peek().ch) == -1) {queue.poll();}}}return queue.isEmpty() ? -1 : queue.poll().pos;}class Pair {char ch;int pos;Pair(char ch, int pos) {this.ch = ch;this.pos = pos;}}
}