用递归实现的，没有stackoverflow但是tle了

#include <stdio.h>

int isHorse(int x, int y, int x_horse, int y_horse);
int abs(int n);
int routeNumbers(int x, int y, int x_horse, int y_horse, int n, int m);

int main(int argc, char const *argv[]) {
  int x_horse, y_horse, n, m, num;
  scanf("%d%d%d%d", &n, &m, &x_horse, &y_horse);
  num = routeNumbers(0, 0, x_horse, y_horse, n, m);
  printf("%d", num);

  return 0;
}

int isHorse(int x, int y, int x_horse, int y_horse) {
  return (abs(x - x_horse) == 2 && abs(y - y_horse) == 1) ||
         (abs(x - x_horse) == 1 && abs(y - y_horse) == 2) ||
         (x == x_horse && y == y_horse);
}

int abs(int n) { return n < 0 ? -n : n; }

int routeNumbers(int x, int y, int x_horse, int y_horse, int n, int m) {
  int num = 0;
  if ((x == n) && (y == m))
    num++;
  else if (!isHorse(x, y, x_horse, y_horse)) {
    if (x < n) num += routeNumbers(x + 1, y, x_horse, y_horse, n, m);
    if (y < m) num += routeNumbers(x, y + 1, x_horse, y_horse, n, m);
  }
  return num;
}