Spiral Matrix

Write a C program that, given an M x N matrix, returns all elements of the matrix in spiral order. The spiral starts at the top-left corner of the matrix and proceeds in a clockwise direction, gradually moving inward until all elements have been visited.

Example 1

  
Input: 
    matrix = [
      [1, 2, 3],
      [4, 5, 6],
      [7, 8, 9]
    ]
  
  
Output: [1, 2, 3, 6, 9, 8, 7, 4, 5]
  
Explanation: 
    

      
Step 1: Start at the top-left corner (1).
      
Step 2: Move right until the end of the first row (1 -> 2 -> 3).
      
Step 3: Move down until the end of the last column (3 -> 6 -> 9).
      
Step 4: Move left until the start of the last row (9 -> 8 -> 7).
      
Step 5: Move up until the start of the first column excluding the visited element (7 -> 4).
      
Step 6: Continue spiraling inward (4 -> 5).
      
Step 7: All elements have been visited, return the spiral order.
    
  

Example 2

  
Input: 
    matrix = [
      [1, 2, 3, 4],
      [5, 6, 7, 8],
      [9, 10, 11, 12]
    ]
  
  
Output: [1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7]
  
Explanation: 
    

      
Step 1: Start at the top-left corner (1).
      
Step 2: Move right until the end of the first row (1 -> 2 -> 3 -> 4).
      
Step 3: Move down until the end of the last column (4 -> 8 -> 12).
      
Step 4: Move left until the start of the last row (12 -> 11 -> 10 -> 9).
      
Step 5: Move up until the start of the first column excluding the visited element (9 -> 5).
      
Step 6: Continue spiraling inward (5 -> 6 -> 7).
      
Step 7: All elements have been visited, return the spiral order.
    
  

Constraints

  
m == matrix.length
  
n == matrix[i].length
  
1 <= m, n <= 10
  
-100 <= matrix[i][j] <= 100
  
Time Complexity: O(m*n) where m is the number of rows and n is the number of columns
  
Space Complexity: O(1) excluding the output array