LC : https://leetcode-cn.com/problems/he-wei-sde-liang-ge-shu-zi-lcof/
    牛客：https://www.nowcoder.com/practice/390da4f7a00f44bea7c2f3d19491311b?tpId=13&&tqId=11195&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

    1. 双指针，一个从左，一个从右遍历，两数之和大于target 的话 right--, 两数之和小于target的话 left++
    1. class Solution {
    2. public:
    3.     vector<int> twoSum(vector<int> &nums, int target) {
    4.         int left = 0, right = nums.size() - 1;
    5.         while (left < right) {
    6.             int calc = nums[left] + nums[right];
    7.             if (calc == target) {
    8.                 return vector<int>{nums[left], nums[right]};
    9.             } else if (calc > target) {
    10.                 right--;
    11.             } else {
    12.                 left++;
    13.             }
    14.         }
    15.         return vector<int>{-1, -1};
    16.     }
    17. };