bktr 13.6

#include <stdio.h>
#include <stdlib.h>
#define NMAX 100

void bktr(int top, int n, int d, int sum, int last, int *cnt) {
  if (sum == d && top == n) {
    ++*cnt;
    return;
  }
  if (sum > d || top > n) {
    return;
  }
  for (int i = last + 1; i <= d; i++) {
    bktr(top + 1, n, d, sum + i, i, cnt);
  }
}

int main() {
  int d, n;
  scanf("%d%d", &d, &n);
  int cnt = 0;
  bktr(0, n, d, 0, 0, &cnt);
  printf("%d\n", cnt);
 return 0;
}