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C. binary search.cpp
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C. binary search.cpp
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#include <fstream>
#include <string>
#include <iostream>
#include <math.h>
#include <algorithm>
#include<bits/stdc++.h>
#include <vector>
using namespace std;
int num, n, pos;
int mod = 1000000007;
int main(){
cin >> n >> num >> pos;
int arr[n];
arr[pos] = num;
for (int x = 0; x < pos; x++){
arr[x] = num - 1;
}
for (int x = pos + 1; x < n; x++){
arr[x] = num + 1;
}
vector<int> bigger;
vector<int> smaller;
int left = 0;
int right = n;
while(left < right){
int middle = (left + right)/2;
if (arr[middle] <= num){
left = middle + 1;
smaller.push_back(middle);
}
else{
right = middle;
bigger.push_back(middle);
}
}
if (bigger.size() > n - num){
cout << 0 << "\n";
return 0;
}
if (smaller.size() - 1 >= num){
cout << 0 << "\n";
return 0;
}
long long cur = num - 1;
long long answer = 1;
for (int x = 0; x < smaller.size() - 1; x++){
answer = (answer * cur) % mod;
cur--;
}
cur = n - num;
for (int x = 0; x < bigger.size(); x++){
answer = (answer * cur) % mod;
cur--;
}
cur = n - smaller.size() - bigger.size();
while(cur > 0){
answer = (answer * cur) % mod;
cur--;
}
cout << answer << "\n";
}