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].

Map作为寄存器，避免多次循环

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