leetcode 1. Tow Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.


You may assume that each input would have exactly one solution, and you may not use the same element twice.


Example:
Given nums = [2, 7, 11, 15], target = 9,


Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int n = nums.length;
        int[] a= new int[2];
        if (n < 2) 
            return a;
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < n; i++) {
            if (!map.isEmpty() && map.containsKey(target - nums[i])) {
                a[0] = i;
                a[1] = map.get(target - nums[i]);
            }
            map.put(nums[i], i);
        }
        return a;
    }
}