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矩阵乘法 --- hdu 4920 ： Matrix multiplication

2024-07-16 00:12:43   222人阅读

Matrix multiplication

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 820    Accepted Submission(s): 328


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
 
 

 

Mean:

给你两个矩阵，计算两个矩阵的积。

 

nalyse:

很多人认为这题用暴力过不了，时间复杂度为O(n^3),800^3=512000000，差不多要接近于10^9了，可能是hdu的评测速度给力吧，再加上这题是单点评测，每个评测点的时限都有2000ms，所以说暴力过了也实属正常。

 

Time complexity：O(n^3)

 

Source code：

#include<stdio.h>int a[800][800],b[800][800],c[800][800],n,i,j,k;int main(){    while(scanf("%d",&n)!=EOF){        for(i=0;i<n;++i)            for(j=0;j<n;++j)                scanf("%d",&a[i][j]),a[i][j]%=3;        for(i=0;i<n;++i)            for(j=0;j<n;++j)                scanf("%d",&b[i][j]),b[i][j]%=3;        for(i=0;i<n;++i)            for(j=0;j<i;++j)                k=b[i][j],b[i][j]=b[j][i],b[j][i]=k;        for(i=0;i<n;++i)            for(j=0;j<n;++j){                c[i][j]=0;                for(k=0;k<n;++k)                    c[i][j]+=a[i][k]*b[j][k];                c[i][j]%=3;            }        for(i=0;i<n;++i)            for(j=0;j<n;++j)                printf(j==n-1?"%d\n":"%d ",c[i][j]);    }    return 0;}

　　

 


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