Program to print matrix elements in spiral order in python

Suppose we have a 2D matrix mat. We have to print the matrix elements in a spiral way. At first starting from the first row (mat[0, 0]), print the whole content and then follow the last column to print, then the last row, and so on, thus it prints the elements in a spiral fashion.

So, if the input is like

then the output will be [7, 10, 9, 1, 3, 4, 5, 11, 9, 9, 2, 9, 6, 2, 9, 2, 1, 7]

To solve this, we will follow these steps:

• d := 0
• top := 0, down := row count of matrix – 1, left := 0, right := column count of matrix - 1
• c := 0
• res := a new list
• direction := 0
• while top <= down and left <= right, do
  • if direction is same as 0, then
    • for i in range left to right + 1, do
      • insert matrix[top, i] into res
    • top := top + 1
  • if direction is same as 1, then
    • for i in range top to down + 1, do
      • insert matrix[i, right] into res
    • right := right - 1
  • if direction is same as 2, then
    • for i in range right to left - 1, decrease by 1, do
      • insert matrix[down, i] into res
    • down := down - 1
  • if direction is same as 3, then
    • for i in range down to top - 1, decrease by 1, do
      • insert matrix[i, left] into res
    • left := left + 1
• direction :=(direction + 1) mod 4
• return res

Let us see the following implementation to get better understanding:

Example

Live Demo

class Solution:
   def solve(self, matrix):
      d = 0
      top = 0
      down = len(matrix) - 1
      left = 0
      right = len(matrix[0]) - 1
      c = 0
      res = []
      direction = 0
      while top <= down and left <= right:
         if direction == 0:
            for i in range(left, right + 1):
               res.append(matrix[top][i])
               top += 1

         if direction == 1:
            for i in range(top, down + 1):
               res.append(matrix[i][right])
            right -= 1

         if direction == 2:
            for i in range(right, left - 1, -1):
               res.append(matrix[down][i])
            down -= 1

         if direction == 3:
            for i in range(down, top - 1, -1):
               res.append(matrix[i][left])
            left += 1

         direction = (direction + 1) % 4
      return res

ob = Solution()
matrix = [
   [7, 10, 9],
   [2, 9, 1],
   [6, 2, 3],
   [9, 1, 4],
   [2, 7, 5],
   [9, 9, 11]
]
print(ob.solve(matrix))

Input

[    
[7, 10, 9],    
[2, 9, 1],    
[6, 2, 3],    
[9, 1, 4],    
[2, 7, 5],    
[9, 9, 11]
]

Output

[7, 10, 9, 1, 3, 4, 5, 11, 9, 9, 2, 9, 6, 2, 9, 2, 1, 7]

Arnab Chakraborty

Updated on: 26-Nov-2020

2K+ Views

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