TwoSum.java

/**
 * @author eko
 * @date 2018/10/20 12:12 PM
 *
 * 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].
 *
 */

package leetcode;

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

public class TwoSum {
    public static void main(String[] args) {
        int[] nums = {2, 7, 11, 15};
        int target = 9;
        int[] res = new TwoSum().twoSum(nums, target);
        for (int i = 0; i < res.length; i++) {
            System.out.println(i);
        }
    }

    public int[] twoSum(int[] nums, int target) {
        int[] res = new int[2];
        Map<Integer,Integer> map = new HashMap<>();

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