1. (寻找被移除的元素)问题: 原有长度为 $n+1$ 公差为 $1$ 等差数列，将数列输到程序的数组时移除了一个元素，导致长度为 $n$ 的连续数组可能不再连续，除非被移除的是第一个或最后一个元素。需要在数组不连续时，找出被移除的元素。试补全程序。

1#include <iostream>2#include <vector>3using namespace std;4int find_missing(vector<int>& nums) {5    int left = 0, right = nums.size() - 1;6    while (left < right){7        int mid = left + (right - left) / 2;8        if (nums[mid] == mid + ①) {9            ②;10        } else {11            ③;12        }13    }14    return ④;15}16int main() {17    int n;18    cin >> n;19    vector<int> nums(n);20    for (int i = 0; i < n; i++) cin >> nums[i];21    int missing_number = find_missing(nums);22    if (missing_number == ⑤) {23        cout << "Sequence is consecutive" << endl;24    }else{25        cout << "Missing number is " << missing_number << endl;26    }27    return 0;28}