• 如：1，3，3，3，5，6，8，9
• 找左端点的3：
  • mid = (right - left) / 2 + left;
  • if(nums[mid] < key)
    left = mid + 1;
    else
    right = mid;
• 找右端点的3：
  • mid = (right - left) / 2 + left + 1;
  • if(nums[mid] > key)
    right = mid - 1;
    else
    left = mid;

#include <iostream>
#include <vector>using namespace std;int find_left(const vector<int>& nums, int left, int right, int key)
{while(left < right){int mid = (right - left) / 2 + left;if(nums[mid] < key){left = mid + 1;}else{right = mid;}}return nums[left] == key ? left : -1;
}int find_right(const vector<int>& nums, int left, int right, int key)
{while(left < right){int mid = (right - left) / 2 + left + 1;if(nums[mid] > key){right = mid - 1;}else{left = mid;}}return nums[left] == key ? left : -1;
}
int main()
{int n, k;cin >> n >> k;vector<int> nums(n), qry(k);for(int i = 0; i < n; i++)cin >> nums[i];for(int i = 0; i < k; i++)cin >> qry[i];//cout << find_left(nums, 0, n - 1, qry[2]);//cout << find_right(nums, 0, n - 1, qry[1]);for(auto &a : qry){cout << find_left(nums, 0, n - 1, a) << " ";cout << find_right(nums, 0, n - 1, a) << endl;}return 0;
}