C++ 中求解方程 x1 + x2 +…. + xN = k 的整数解个数

#include <bits/stdc++.h>
using namespace std;
int factorial(int n) {
   int product = 1;
   for (int i = 2; i <= n; i++) {
      product *= i;
   }
   return product;
}
int nCr(int n, int r) {
   return factorial(n) / (factorial(n - r) * factorial(r));
}
int main() {
   int n = 4;
   int k = 7;
   cout << nCr(n + k - 1, k) + nCr(k - 1, n - 1) &l<t; endl;
   return 0;
}