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]
// Output: 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 <= 105
// -109 <= nums[i] <= 109
// -109 <= target <= 109
// Only one valid answer exists.

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