Unique Paths III @LeetCode

Just to wake up; 

980. Unique Paths III
https://leetcode.com/problems/unique-paths-iii/

class Solution:

    

    def checkIfReachable(self,curPoint,walkable, grid):

        (i,j) = curPoint

        #print(curPoint)

        if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]):

            return 0

        

        if grid[i][j]==2:

            if len(walkable)==0:

                return 1

            else:

                return 0

        

        if curPoint not in walkable:

            return 0

        

        walkable.remove(curPoint)

        

        num1 = self.checkIfReachable((i+1,j  ),walkable.copy(),grid)

        num2 = self.checkIfReachable((i-1,j  ),walkable.copy(),grid)

        num3 = self.checkIfReachable((i  ,j+1),walkable.copy(),grid)

        num4 = self.checkIfReachable((i  ,j-1),walkable.copy(),grid)

        

        return num1+num2+num3+num4

    

    def uniquePathsIII(self, grid: List[List[int]]) -> int:

        

        walkable = []

        

        for i in range(len(grid)):

            for j in range(len(grid[0])):

                if grid[i][j] == 0:

                    walkable.append((i,j))

                elif grid[i][j] == 1:

                    walkable.append((i,j))

                    start = (i,j)

        

        numPath = self.checkIfReachable(start,walkable,grid)

        return numPath