ACM POJ 2356

Find a multiple

Time Limit: 1000MS
Memory Limit: 65536KB
64bit IO Format: %I64d & %I64u

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Description

The input contains N natural (i.e. positive integer) numbers ( N <= 10000 ). Each of that numbers is not greater than 15000. This numbers are not necessarily different (so it may happen that two or more of them will be equal). Your task is to choose a few of given numbers ( 1 <= few <= N ) so that the sum of chosen numbers is multiple for N (i.e. N * k = (sum of chosen numbers) for some natural number k).

Input

The first line of the input contains the single number N. Each of next N lines contains one number from the given set.

Output

In case your program decides that the target set of numbers can not be found it should print to the output the single number 0. Otherwise it should print the number of the chosen numbers in the first line followed by the chosen numbers themselves (on a separate line each) in arbitrary order.
If there are more than one set of numbers with required properties you should print to the output only one (preferably your favorite) of them.

Sample Input

5
1
2
3
4
1

Sample Output

2
2
3

Source

Ural Collegiate Programming Contest 1999

抽屉原理，开始高明白，安叔一点拨就清楚了，Orz，和mod后相同的两个数就可以

给代码了

#include <cstdio>
#include <cstring>
const int N = 10001;
int a[N],sum[N],visit[N] ;

int n;

void print(int i,int j)
{
    printf("%d
",j-i+1);
    int k;
    for(k=i; k<=j; k++)
    {
        printf("%d
",a[k]);
    }
    return ;
}

int main()
{

    scanf("%d",&n);
    sum[0] = 0;
    memset(visit,0,sizeof(visit));
    for(int i=1; i<=n; i++)
    {
        scanf("%d",&a[i]);
        sum[i] = (a[i] + sum[i-1]) % n;
    }
//    for(int i = 1; i <=n; i++)
//    {
//        printf("%d
",sum[i]);
//    }
    for(int i = 1; i<=n; i++)
    {
        if(sum[i] == 0)
        {
            print(1,i);
            return 0;
        }
        else
        {
            if(visit[sum[i]]!= 0)
            {
                print((visit[sum[i]]+1),i);
                return 0;
            }
            else
            {
                visit[sum[i]]=i;
//                printf("%d
",visit[i]);
            }
        }

    }
}