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Program to find the perimeter of an island shape in Python

Suppose we have a binary matrix where 0 shows empty cell and 1 shows a block that forms a shape, now we have to find the perimeter of the shape. The shape will not hold any hole inside it.

So, if the input is like

00000
00111
00110
01110
00000

then the output will be 14.

To solve this, we will follow these steps −

  • d := 0

  • perimeter := 0

  • height := row count of matrix

  • length := column count of matrix

  • for each row in matrix, do

    • c := 0

    • for each val in row, do

      • if val is same as 1, then

        • surround := 4

        • if c is not same as length - 1, then

          • if matrix[d, c + 1] is same as 1, then

            • surround := surround - 1

        • if c is not same as 0, then

          • if matrix[d, c - 1] is same as 1, then

            • surround := surround - 1

        • if d is not same as height - 1, then

          • if matrix[d + 1, c] is same as 1, then

            • surround := surround - 1

        • if d is not same as 0, then

          • if matrix[d - 1, c] is same as 1, then

            • surround := surround - 1

        • perimeter := perimeter + surround

        • c := c + 1

    • d := d + 1

  • return perimeter

Let us see the following implementation to get better understanding −

Example

class Solution:
   def solve(self, matrix):
      d = 0
      perimeter = 0
      height = len(matrix)
      length = len(matrix[0])
      for line in matrix:
         c = 0

         for val in line:
            if val == 1:
               surround = 4
               if c != length - 1:
                  if matrix[d][c + 1] == 1:
                     surround -= 1
               if c != 0:
                  if matrix[d][c - 1] == 1:
                     surround -= 1
               if d != height - 1:
                  if matrix[d + 1][c] == 1:
                     surround -= 1
               if d != 0:
                  if matrix[d - 1][c] == 1:
                     surround -= 1
               perimeter += surround
            c += 1
         d += 1
      return perimeter

ob = Solution()
matrix = [
   [0,0,0,0,0],
   [0,0,1,1,1],
   [0,0,1,1,0],
   [0,1,1,1,0],
   [0,0,0,0,0]
]
print(ob.solve(matrix))

Input

matrix = [
[0,0,0,0,0],
[0,0,1,1,1],
[0,0,1,1,0],
[0,1,1,1,0],
[0,0,0,0,0]]

Output

14