Two Sum

Link

A pretty straightforward solution. Use a HashMap with the key representing the

(target-nums[i])  

and the value representing the index at which it appeared.

Full Solution in Java:

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

    HashMap<Integer,Integer> values = new HashMap<Integer,Integer>();    
    int[] retArr = new int[2];
    
    for(int i=0; i<nums.length; i++){

        if(values.containsKey(nums[i])){
            retArr[0] = values.get(nums[i]);
            retArr[1] = i;
            break;
        }
        else{
            values.put(target-nums[i], i);
        }
    }
    return retArr;
  }
}