poj 1775 Sum of Factorials

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;int fac[20];bool f[1000005];int tot;void dfs(int i, int sum){    if (sum > 1000000)        return;    f[sum] = true;    if (i == tot)        return;    dfs(i + 1, sum + fac[i]);    dfs(i + 1, sum);}int main(){    fac[0] = 1;    tot = 0;    for (int i = 1; fac[i - 1] <= 1000000; i++)    {        fac[i] = fac[i - 1] * i;        tot++;    }    memset(f, 0, sizeof(f));    dfs(0, 0);    int n;    while (scanf("%d", &n), n >= 0)        if (f[n] && n != 0) printf("YESn");        else printf("NOn");    return 0;}