1. Two Sum

题目：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.
Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

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