牛客网 Matrix Multiplication（数学）

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本文介绍了一个简单的矩阵乘法计算器的设计与实现。该计算器能够接收两个矩阵作为输入，并判断它们是否可以相乘。若可以，则输出乘法结果；若维度不匹配，则返回错误提示。文章包含完整的C++代码示例。

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链接：https://www.nowcoder.com/acm/contest/163/K
来源：牛客网
题目描述
In mathematics, matrix multiplication or matrix product is a binary operation that produces a matrix from two matrices with entries in a field, or, more generally, in a ring or even a semiring. The matrix product is designed for representing the composition of linear maps that are represented by matrices. Matrix multiplication is thus a basic tool of linear algebra, and as such has numerous applications in many areas of mathematics, as well as in applied mathematics, physics, and engineering. In more detail, if A is an n x m matrix and B is an m x p matrix, their product AB is an n x p matrix, in which the m entries across a row of A are multiplied with the m emtries down a column of B and summed to produce an entry of AB. When two linear maps are represented by matrices, then the matrix product represents the composition of the two maps.
We can only multiply two matrices if their dimensions are compatible, which means the number of columns in the first matrix is the same as the number of rows in the second matrix.
这里写图片描述
Your task is to design a matrix multiplication calculator to multiply two matrices and
display the output. If the matrices cannot be multiplied, display “ERROR”.
输入描述:
The first line of the input is T(1≤ T ≤ 100), which stands for the number of test cases you need to solve.
For each test case, the first line contains four integers m, n, p and q (1 ≤ m,n,p,q ≤ 20). m and n represent the dimension of matrix A, while p and q represent the dimension of matrix B.
The following m lines consist of the data for matrix A followed by p lines that contains the data for matrix B. (-100 ≤ aij ≤ 100, -100 ≤ bij ≤ 100).
输出描述:
For each test case, print the case number and the output of the matrix multiplication.
示例1
输入
复制
2
2 3 3 2
1 1 1
1 2 3
2 3
4 5
6 7
2 3 2 3
1 2 3
1 2 3
2 3 4
2 3 4
输出
复制
Case 1:
12 15
28 34
Case 2:
ERROR
矩阵的乘法计算

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int t,k=0;cin>>t;
    while(t--)
    {
        k++;
        int n1,m1,n2,m2;
        int a[25][25],b[25][25],c[25][25];
        cin>>n1>>m1>>n2>>m2;
        for(int i=0;i<n1;i++)
            for(int j=0;j<m1;j++)
                cin>>a[i][j];
        for(int i=0;i<n2;i++)
            for(int j=0;j<m2;j++)
                cin>>b[i][j];
        printf("Case %d:\n",k);
        if(m1!=n2) cout<<"ERROR"<<endl;
        else{
            memset(c,0,sizeof(c));
            for(int i=0;i<n1;i++){
                for(int j=0;j<m2;j++){
                    for(int x=0;x<m1;x++)
                    c[i][j]+=a[i][x]*b[x][j];
                }
            }
            for(int i=0;i<n1;i++){
                for(int j=0;j<m2;j++){
                    cout<<c[i][j]<<" ";
                }
                cout<<endl;
            }
        }
    }
}