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hdu 4920 Matrix multiplication bitset优化常数

2024-08-30 11:23:27   239人阅读

Matrix multiplication

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)


Problem Description
Given two matrices A and B of size n×n, find the product of them.

bobo hates big integers. So you are only asked to find the result modulo 3.
 

 

Input
The input consists of several tests. For each tests:

The first line contains n (1≤n≤800). Each of the following n lines contain n integers -- the description of the matrix A. The j-th integer in the i-th line equals Aij. The next n lines describe the matrix B in similar format (0≤Aij,Bij≤109).
 

 

Output
For each tests:

Print n lines. Each of them contain n integers -- the matrix A×B in similar format.
 

 

Sample Input
10120 12 34 56 7
 

 

Sample Output
00 12 1
 

 

Author
Xiaoxu Guo (ftiasch)
 

 

Source
2014 Multi-University Training Contest 5
题意：给你两个矩阵，求矩阵相乘%3；
思路：正常思路n*n*n求解（运气好可以ac。。。），看了下数据范围由于mod=3，所以利用bitset标记每行1，2，0的位置，取并集就可以得到相同位置的个数；
　　　这样就可以优化最后的一个n。详见代码；
#include<bits/stdc++.h>using namespace std;#define ll long long#define pi (4*atan(1.0))#define eps 1e-14const int N=1e3+10,M=1e6+10,inf=1e9+10;const ll INF=1e18+10,mod=2147493647;int n;bitset<N>a[N][5],b[N][5];int ans(int i,int j){    int u=(a[i][1]&b[j][1]).count(),v=(a[i][1]&b[j][2]).count();    int x=(a[i][2]&b[j][1]).count(),y=(b[j][2]&a[i][2]).count();    return u+v*2+x*2+y*4;}int main(){    while(~scanf("%d",&n))    {        for(int i=0;i<n;i++)            for(int j=0;j<=3;j++)            a[i][j].reset(),b[i][j].reset();        for(int i=0; i<n; i++)            for(int j=0; j<n; j++)            {                int x;                scanf("%d",&x);                a[i][x%3].set(j);            }        for(int i=0; i<n; i++)            for(int j=0; j<n; j++)            {                int x;                scanf("%d",&x);                b[j][x%3].set(i);            }        for(int i=0;i<n;i++)        {            for(int j=0;j<n;j++)                printf("%d%c",ans(i,j)%3,(j!=n-1?‘ ‘:‘\n‘));        }    }    return 0;}

 

hdu 4920 Matrix multiplication bitset优化常数


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