POJ1613 147/思维题

#include<bits/stdc++.h>
using namespace std;
typedef long long  LL;
const int maxn = 30;
const int mod = 1e9+7;
int a[5]={0,1,4,7};
int ans[maxn];
int k;
int main ()
{
    while(~scanf("%d",&k))
    {
        int len=0;
        while(k)
        {
            int t=k%3;
            if(t==0) t=3;
            ans[++len]=a[t];
            k=(k-t)/3;
        }
        for(int i=len;i>=1;i--)
            printf("%d",ans[i]);
        printf("\n");
    }
    return 0;
}