Find a Symmetric matrix of order N that contain integers from 0 to N-1 and main diagonal should contain only 0’s

Given an integer N. The task is to generate a symmetric matrix of order N*N having the following properties. 
 

1. Main diagonal should contain only 0’s
2. The matrix should contain elements from 0 to N-1 only.

Examples: 
 

Input: N = 4 
Output: 
0 2 3 1 
2 0 1 3 
3 1 0 2 
1 3 2 0
Input: N = 5 
Output: 
0 2 3 4 1 
2 0 4 1 3 
3 4 0 2 1 
4 1 2 0 3 
1 3 1 3 0 
 

Approach: Since the required matrix has to be a square matrix, we can generate a symmetric matrix containing an element from 1 to n-1, excluding 0. We will deal with the case of 0 later. 
Take for example when N = 4: 
We first generate a symmetric matrix, and it can be easily done by filling every row from 1 to n-1 in cyclic order, i.e. fill the first row by 1 2 3, and do this for all subsequent rows in cyclic order. 
 

So, the final matrix will be, 
1 2 3 
2 3 1 
3 1 2 
 

Now, we have generated a symmetric matrix containing elements from 1 to n. Let’s discuss case 0. We will take the benefit of the above matrix being symmetrical, we will add a column of 0 and rows of 0 like this, 
 

1 2 3 0 
2 3 1 0 
3 1 2 0 
0 0 0 0 
 

Now, we have to put all 0 in diagonal. For this, we will start with the first row till last-1 row and swap all the 0 with the number that is there in each row and will also make a change in the last row like this: 
 

For row 1, we swap 0 and 1 and also put last row’s 1st element with the number we swapped i.e. 1. 
0 2 3 1 
2 3 1 0 
3 1 2 0 
1 0 0 0
For row 2 we swap 0 and 3, and make the second element of the last row also 3. 
0 2 3 1 
2 0 1 3 
3 1 2 0 
1 3 0 0 
and so on… 
The final matrix generated will be the required matrix. 
 

Below is the implementation of the above approach: 
 

0 2 3 4 1 
2 0 4 1 3 
3 4 0 2 1 
4 1 2 0 3 
1 3 1 3 0 

Time Complexity: O(N²)

Auxiliary Space: O(N²)