两数之和

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