Two 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) {
        TreeMap<Integer, Integer> map = new TreeMap<>();
        int[] output = new int[2];
        for (int i = 0; i < nums.length; i++) {
            int num = nums[i];
            if (map.containsKey(target - num)){
                output[0] = map.get(target-num);
                output[1] = i;
                return output;
            } else {
                map.put(num, i);
            }
        }
        return output;
    }
}