求一个数组中和为指定值的2个元素下标值

int[] sum2Num(int[] nums, int target) {
        int length = nums.length;
        Map<Integer, Integer> map = new HashMap<>(length);
        for (int i = 0; i < length; i++) {
            Integer n = nums[i];
            Integer otherNum = target - n;
            if (map.containsKey(otherNum)) {
                // bingo
                return new int[]{i, map.get(otherNum)};
            }
            map.put(n, i);
        }
        return new int[]{};
    }