AtCoder. ABC 237 B Matrix Transposition

Problem: AtCoder ABC 237 B — Matrix Transposition

Given an H by W matrix A, output its transpose B, which has W rows and H columns. Transposition swaps each element’s row and column indices: for every 0 <= i < H and 0 <= j < W, set B[j][i] = A[i][j]. The dimensions need not be equal, so the output must be built with W rows of H values each; this also handles a single row or column naturally.

The constraints are small (1 <= H, W <= 100), and every input value can be copied once into its transposed position. The time and storage required are both O(HW). The code reads the dimensions and matrix, then prints each output row with spaces between values and a newline after the row.

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));
        StringTokenizer st = new StringTokenizer(br.readLine());
        int h = Integer.parseInt(st.nextToken());
        int w = Integer.parseInt(st.nextToken());
        int[][] a = new int[h][w];

        for (int i = 0; i < h; i++) {
            st = new StringTokenizer(br.readLine());
            for (int j = 0; j < w; j++) {
                a[i][j] = Integer.parseInt(st.nextToken());
            }
        }

        StringBuilder out = new StringBuilder();
        for (int j = 0; j < w; j++) {
            for (int i = 0; i < h; i++) {
                if (i > 0) out.append(' ');
                out.append(a[i][j]);
            }
            out.append('\n');
        }
        System.out.print(out);
    }
}