TwoSum.java

package Leetcode;

import java.util.HashMap;
import java.util.Map;

/**
 * @author kalpak
 *
 * 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.
 *
 */
public class TwoSum {
    public static int[] twoSum(int[] nums, int target) {
        int[] result = new int[2];
        Map<Integer, Integer> map = new HashMap<>();

        for(int i = 0; i < nums.length; i++) {
            if(map.containsKey(target - nums[i])) {
                result[1] = i;
                result[0] = map.get(target - nums[i]);
                break;
            }
            map.put(nums[i], i);
        }
        return result;
    }

    public static void main(String[] args) {
        int[] arr = new int[]{2,7,11,15};
        int[] result = twoSum(arr, 9);
        for(int i : result)
            System.out.print(i + " ");
        System.out.println();
    }
}