class Solution {
    public int singleNumber(int[] nums) {
        int index = 0;
        Map<Integer, Integer> map = new HashMap<>();
        for (int num : nums) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        for (Map.Entry<Integer, Integer> integerIntegerEntry : map.entrySet()) {
            if (integerIntegerEntry.getValue() == 1) {
                return integerIntegerEntry.getKey();
            }
        }
        return -1;
    }
}

原文链接： https://leetcode-cn.com/problems/shu-zu-zhong-shu-zi-chu-xian-de-ci-shu-ii-lcof/