Matrix

A matrix is a two-dimensional array or table, which can be represented as a grid of rows and columns. A single value which is an intersection of a row and a column is called a cell, which is usually accessed by row and column indices

Corner Cases

• Empty matrix, one of the arrays of length 0
• 1 by 1 matrix
• one row/ one column matrix

Techniques

Creating an n by m Matrix

Creating a matrix of specified dimensions is often useful when dealing with graph traversal or dynamic programming.

int[][] matrix = new int[n][m];

new_matrix = [[0 for _ in range(len(matrix[0]))] for _ in range(len(matrix))]

Copying an Existing Matrix

int [][] newMatrix = new int[matrix.length][]
for(int i=0; i<matrix.length;i++) {
	newMatrix[i] = matrix[i].clone();
}

copied_matrix = [row[:] for row in matrix]

Transposing a Matrix

Transposing a matrix is done by interchanging its rows into columns. It can be useful if you have to do an operation on both rows and columns, you can then create one function, transpose the matrix and run it again.

int[][] result = new int[mat[0].length][mat.length];
for (int i = 0; i < mat.length; ++i) {
	for (int j = 0; j < mat[0].length; ++j) {
		result[j][i] = mat[i][j];
	}
}

transposed_matrix = zip(*matrix)