1 Two Sum.java

// Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

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

// You can return the answer in any order.

 
// Example 1:

// Input: nums = [2,7,11,15], target = 9
// Output: [0,1]
// Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
// Example 2:

// Input: nums = [3,2,4], target = 6
// Output: [1,2]
// Example 3:

// Input: nums = [3,3], target = 6
// Output: [0,1]
 

// Constraints:

// 2 <= nums.length <= 104
// -109 <= nums[i] <= 109
// -109 <= target <= 109
// Only one valid answer exists.
 
class Solution {
    public int[] twoSum(int[] nums, int target) {

        Map<Integer,Integer> hash = new HashMap<>(); 
        int comp;

        for(int i = 0; i< nums.length; i++){           
            comp = target - nums[i];

            if(hash.containsKey(comp)){            
                return new int [] {i,hash.get(comp)};
            }
            hash.put(nums[i],i);
        }

        return new int [] {};        
    }
}