[LeetCode] 1. 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].

public int[] twoSum(int[] nums, int target) {

    HashMap<Integer, Integer> map = new HashMap();

    for (int i = 0; i < nums.length; i++) {

        int diff = target - nums[i];

        if (map.containsKey(diff)) return new int[] { map.get(diff), i };

        map.put(nums[i], i);

    }

    return null;

}