PPA-8

Question

An identity matrix is a square matrix which has ones on the main diagonal and zeros everywhere else. For example, the identity matrix of size \(3 \times 3\) is: \[ \begin{bmatrix} 1 & 0 & 0\\ 0 & 1 & 0\\ 0 & 0 & 1 \end{bmatrix} \]

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Accept a positive integer \(n\) as input and print the identity matrix of size \(n \times n\). Your output should have \(n\) lines, where each line is a sequence of \(n\) comma-separated integers that corresponds to one row of the matrix.

Hint

In order to print the elements of a matrix with one row on each line, a nested loop is needed. After the inner loop goes through a row, a new line should be added. This can be done with a simple print statement.

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for i in range(3):
    for j in range(3):
        print(matrix[i][j], end = ',')
    print()

This gives the following output:

1,2,3,
4,5,6,
7,8,9,

How does one get rid of the comma at the end? Check out PPA-5 to get the logic for this.

Solution

n = int(input())
I = [ ]
for i in range(n):
    row = [ ]
    for j in range(n):
        if i == j:
            row.append(1)
        else:
            row.append(0)
    I.append(row)
    
for i in range(n):
    for j in range(n):
        if j != n - 1:
            print(I[i][j], end = ',')
        else:
            print(I[i][j])

Video Solution