• 1.双指针 => O(logN)(排序)

class Solution {
public:
    vector<int> findNumbersWithSum(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        int i = 0, j = nums.size() - 1;
        while (i < j && nums[j] > target) --j;

        while (i < j)
        {
            int res = nums[i] + nums[j] - target;
            if (!res) return {nums[i], nums[j]};
            else if (res > 0) --j;
            else ++i;
        }
        return {};
    }
};

• 2.set => O(n)时间，O(n)空间

class Solution {
public:
    vector<int> findNumbersWithSum(vector<int>& nums, int target) {
        unordered_set<int> set {};
        for (auto &i : nums) { 
            if (set.count(target-i) > 0) return {target-i, i};   
            if (set.count(i) == 0) 
                set.insert(i);
        }

        return {};
    }
};