_1.java

package com.fishercoder.solutions;

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

/**
 * 1. Two Sum
 *
 * 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].
 */
public class _1 {

    public int[] twoSum_ON(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap();
        int[] result = new int[2];
        for(int i = 0; i < nums.length; i++){
            if(map.containsKey(target-nums[i])){
                result[0] = map.get(target-nums[i]);
                result[1] = i;
                break;
            } else {
                map.put(nums[i], i);
            }
        }
        return result;
    }

    public int[] twoSum_ON2(int[] nums, int target) {
        int[] result = new int[2];
        for(int i = 0; i < nums.length-1; i++){
            for(int j = i+1; j < nums.length; j++){
                if(nums[i] + nums[j] == target){
                    result[0] = i;
                    result[1] = j;
                    break;
                }
            }
        }
        return result;
    }

}