Program to fill with color using floodfill operation in Python

Suppose we have a 2D grid, containing colors as strings "r", "g", and "b". We have to perform floodfill operation at row r, column c with the color target. As we know the Floodfill operation should replace all elements that are both connected to grid[r,c] (up/right/down/left) and have the same color as grid[r,c] with the same color as target.

So, if the input is like


then the output will be


as the red cells connected to grid[0,0] are replaced with green ("g").

To solve this, we will follow these steps −

  • define a new set seen
  • oldcolor := matrix[r, c]
  • Define a function dfs() . This will take i, j
  • if i and j are in the matrix and (i, j) is not seen and matrix[i, j] is same as oldcolor, then
    • add(i, j) of seen
    • matrix[i, j] := target
    • dfs(i + 1, j)
    • dfs(i, j + 1)
    • dfs(i, j - 1)
    • dfs(i - 1, j
  • From the main method, do the following −
  • dfs(r, c)
  • return matrix

Let us see the following implementation to get better understanding −


 Live Demo

class Solution:
   def solve(self, matrix, r, c, target):
      def dfs(i, j):
         if (
            i >= 0
            and i < len(matrix)
            and j >= 0
            and j < len(matrix[0])
            and (i, j) not in seen
            and matrix[i][j] == oldcolor
            seen.add((i, j))
            matrix[i][j] = target
            dfs(i + 1, j)
            dfs(i, j + 1)
            dfs(i, j - 1)
            dfs(i - 1, j)
      seen = set()
      oldcolor = matrix[r][c]
      dfs(r, c)
      return matrix
ob = Solution()
matrix = [ ["r", "r", "r"], ["r", "g", "b"], ["g", "b", "b"] ]
r = 0
c = 0
target = "g"
print(ob.solve(matrix, r, c, target))


matrix = [
["r", "r", "r"],
["r", "g", "b"],
["g", "b", "b"] ]
r = 0
c = 0
target = "g"


[ ['g', 'g', 'g'], ['g', 'g', 'b'], ['g', 'b', 'b']]

Updated on: 20-Oct-2020


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