[BaekJoon] 2740번 - 행렬 곱셈 [Java][C++]

문제 링크

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1. 문제 풀이

두 행렬의 곱셈을 구현하는 문제로 2차원 배열로 행렬을 다루면 간단하게 해결할 수 있다.

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2. 코드

1. 풀이 [Java]

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb = new StringBuilder();
        StringTokenizer st = new StringTokenizer(br.readLine());

        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());

        int[][] A = new int[N][M];
        for (int i = 0; i < N; i++) {
            st = new StringTokenizer(br.readLine());

            for (int j = 0; j < M; j++) {
                A[i][j] = Integer.parseInt(st.nextToken());
            }
        }

        st = new StringTokenizer(br.readLine());
        M = Integer.parseInt(st.nextToken());
        int K = Integer.parseInt(st.nextToken());

        int[][] B = new int[M][K];
        for (int i = 0; i < M; i++) {
            st = new StringTokenizer(br.readLine());

            for (int j = 0; j < K; j++) {
                B[i][j] = Integer.parseInt(st.nextToken());
            }
        }

        int[][] res = multiply(A, B, N, M, K);
        for (int i = 0; i < res.length; i++) {
            for (int j = 0; j < res[i].length; j++) {
                sb.append(res[i][j]).append(" ");
            }
            sb.append("\n");
        }

        System.out.print(sb);
    }

    static int[][] multiply(int[][] A, int[][] B, int N, int M, int K) {
        int[][] res = new int[N][K];

        for (int i = 0; i < N; i++) {
            for (int j = 0; j < K; j++) {
                for (int k = 0; k < M; k++) {
                    res[i][j] += A[i][k] * B[k][j];
                }
            }
        }

        return res;
    }
}

2. 풀이 [C++]

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m, k;
    cin >> n >> m;

    vector<vector<int>> a(n, vector<int>(m));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> a[i][j];
        }
    }

    cin >> m >> k;
    vector<vector<int>> b(m, vector<int>(k));
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < k; j++) {
            cin >> b[i][j];
        }
    }

    vector<vector<int>> res(n, vector<int>(k));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < k; j++) {
            for (int t = 0; t < m; t++) {
                res[i][j] += a[i][t] * b[t][j];
            }
        }
    }

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < k; j++) {
            cout << res[i][j] << ' ';
        }
        cout << '\n';
    }
}

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