01Two 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].

考点：map映射用来存放键值对，根据键就能查找到值

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