codeforce 375A Divisible by Seven

原题地址：http://codeforces.com/contest/375/problem/A

 

题意：

略

 

题解

构造，数论

 

#include<bits/stdc++.h>

#define clr(x,y) memset((x),(y),sizeof(x))

using namespace std;
typedef long long LL;

const int maxn=1e6;

char s[maxn+5];
vector <int> v={1,6,8,9};

int A[10];
int Count[10];

int main(void)
{
    #ifdef ex
    freopen ("../in.txt","r",stdin);
    //freopen ("../out.txt","w",stdout);
    #endif

    scanf("%s",s);
    int len=strlen(s);

    for (int i=0;i<len;++i)
        ++Count[s[i]-'0'];

    --Count[1];
    --Count[6];
    --Count[8];
    --Count[9];

    do
    {
        //cout<<v[0]<<' '<<v[1]<<endl;
        int tmp=0;
        for (int i=0;i<=3;++i)
            tmp=tmp*10+v[i]; /*****/
        A[tmp%7]=tmp;
    }while (next_permutation(v.begin(),v.end())); /*****/

    int tmp=0;
    for (int i=1;i<=9;++i)
    {
        for (int j=1;j<=Count[i];++j)
        {
            printf("%d",i);
            tmp=(tmp*10+i)%7; /*****/
        }
    }

    tmp=tmp*10000%7;
    tmp=(7-tmp)%7; /************/
    printf("%d",A[tmp]);

    for (int i=1;i<=Count[0];++i)
        printf("0");


}