pku2941 Homogeneous Squares

http://poj.org/problem?id=2941

随机算法

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int a[1234][1234], n, stack[1234];

int check()
{
    int i, j, temp, sum1 = 0, sum2, m;
    for(i=1; i<=n; i++)
    {
        sum1 += a[i][i];
        stack[i] = i;
    }
    m = 300000;
    while(m--)
    {
        sum2 = sum1;
        j = rand()%n+1;
        sum2 -= (a[1][stack[1]] + a[j][stack[j]]);
        temp = stack[j];
        stack[j] = stack[1];
        stack[1] = temp;
        sum2 += (a[1][stack[1]] + a[j][stack[j]]);
        if(sum1 != sum2)
        {
            return 0;
        }
    }
    return 1;
}

int main()
{
    int i, j;
    while(scanf("%d", &n), n)
    {
        for(i=1; i<=n; i++)
        {
            for(j=1; j<=n; j++)
            {
                scanf("%d", &a[i][j]);
            }
        }
        printf(check()? "homogeneous\n": "not homogeneous\n");
    }
    return 0;
}