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].

Code (Java):

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] ans = new int[2];
        
        if (nums == null || nums.length < 2) {
            return ans;
        }
        
        Map<Integer, Integer> map = new HashMap<>();
        
        for (int i = 0; i < nums.length; i++) {
            int comp = target - nums[i];
            
            if (map.containsKey(comp)) {
                ans[0] = map.get(comp);
                ans[1] = i;
                break;
            } else {
                map.put(nums[i], i);
            }
        }
        
        return ans;
    }
}