POJ 3318 Matrix Multiplication(随机算法)

题目链接

随机算法使劲水...srand((unsigned)time(0))比srand(NULL)靠谱很多，可能是更加随机。

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <map>
#include <ctime>
#include <cmath>
using namespace std;
#define LL __int64
int a[501][501],b[501][501],c[501][501];
int main()
{
    int i,j,k,flag,n;
    srand((unsigned)time(0));
    while(scanf("%d",&n)!=EOF)
    {
        for(i = 1; i <= n; i ++)
        {
            for(j = 1; j <= n; j ++)
                scanf("%d",&a[i][j]);
        }
        for(i = 1; i <= n; i ++)
        {
            for(j = 1; j <= n; j ++)
                scanf("%d",&b[i][j]);
        }
        for(i = 1; i <= n; i ++)
        {
            for(j = 1; j <= n; j ++)
                scanf("%d",&c[i][j]);
        }
        flag = 1;
        for(i = 1; i <= 40000&&flag; i ++)
        {
            LL temp = 0;
            int x,y;
            x = rand()%n + 1;
            y = rand()%n + 1;
            for(k = 1; k <= n; k ++)
            {
                temp += a[x][k]*b[k][y];
            }
            if(temp != c[x][y])
                flag = 0;
        }
        if(flag)
            printf("YES
");
        else
            printf("NO
");
    }
    return 0;
}