poj1775

搜索，注意0是NO

#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()
{
    //freopen("t.txt", "r", stdin);
    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("YES\n");
        else
            printf("NO\n");
    return 0;
}