[LeetCode]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].
1.暴力 O(n^2)
2.排序后双指针 O(nlogn)
3.hash o(n)

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