Inplace transpose of a matrix in Java-CodePudding

I'm trying a simple intuition to transpose a matrix in place.

I'm trying to swap elements of matrix[i][j] and matrix[j][i] but it is not working, I'm wondering what is happening behind the scene.

class Solution {
    public int[][] transpose(int[][] matrix) {
        
        
        for(int i = 0; i < matrix.length; i  ){
            for(int j = 0; j < matrix[0].length; j  ){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
        
        return matrix;
    }
}

Output

For matrix -> [[1,2,3],[4,5,6],[7,8,9]]

It is giving output -> [[1,2,3],[4,5,6],[7,8,9]]

but the expected output should be -> [[1,4,7],[2,5,8],[3,6,9]]

CodePudding user response：

You are transposing each pair of elements twice, which puts them back how they were.

One solution would be to change for(int j = 0; in the inner loop to for(int j = i 1;. This would make sure that each pair of elements is only transposed once.

Also be aware that this general solution only works for square matrices.

CodePudding user response：

how about this way?

public int[][] transpose(int[][] matrix) {
    int[][] result = new int[matrix.length][matrix[0].length];
    for(int i = 0; i < matrix[0].length; i  ){
        for(int j = 0; j < matrix.length; j  ){
            result[j][i] = matrix[i][j];
            System.out.println(Arrays.deepToString(result));
        }
    }

    return result;
}