哈希表
class Solution {
public:
    vector<int> findNumbersWithSum(vector<int>& nums, int target) {
        unordered_set<int> hash;
        for(int i = 0;i < nums.size();++i){
            if(hash.count(target - nums[i]))    return {nums[i],target - nums[i]};
            hash.insert(nums[i]);
        }
        return vector<int>();
    }
};