杭电------2048神上帝以及老天爷（C语言写）

#include<stdio.h>
long long a[22] = { -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1 };
long long b[22] = { 0 };
long long jiecheng(int n) {
    if (b[n]>0) {
        return b[n];
    }
    return b[n] = jiecheng(n - 1)*n;
}
long long recrusion(int n) {
    if (a[n] > -1)
        return a[n];
    return a[n] = (n - 1)*(recrusion(n - 2) + recrusion(n - 1));
}

int main() {
    int n, m;
    int i;
    b[0] = 1;
    b[1] = 1;
    a[0] = 1;
    a[1] = 0;
    double x;
    scanf("%d", &n);
    for (i = 0; i < n; i++) {
        scanf("%d", &m);
        x = (double)recrusion(m) / (double)jiecheng(m);
        printf("%.2lf%%
", x * 100);
    }
    return 0;
}（m大于7时概率不再变化）