Escape a Large Maze Python

Suppose we have a grid, there are 1 million rows and 1 million columns, we also have one list of blocked cells. Now we will start at the source square and want to reach the target square. In each move, we can walk to a up, down, left, right adjacent square in the grid that isn't in the given list of blocked cells.

We have to check whether it is possible to reach the target square through a sequence of moves or not.

So, if the input is like blocked = [[0,1],[1,0]], source = [0,0], target = [0,3], then the output will be False

To solve this, we will follow these steps −

  • blocked := make a set of all blocked cells

  • Define one method dfs(), this will take x, y, target and seen

  • if (x,y) are not in range of grids or (x,y) is in blocked or (x,y) is in seen then

    • return false

  • add (x,y) into seen

  • if size of seen > 20000 or (x,y) is target, then

    • return true

  • return dfs(x+1,y,target,seen) or dfs(x-1,y,target,seen) or dfs(x,y+1,target,seen) or dfs(x,y-1,target,seen)

  • return dfs(source[0], source[1], target, empty set) and dfs(target[0], target[1], source, empty set)

Let us see the following implementation to get better understanding −


class Solution(object):
   def isEscapePossible(self, blocked, source, target):
      blocked = set(map(tuple, blocked))
      def dfs(x, y, target, seen):
         if not (0 <= x < 10**6 and 0 <= y < 10**6) or (x, y) in blocked or (x, y) in seen: return             False
         seen.add((x, y))
         if len(seen) > 20000 or [x, y] == target: return True
         return dfs(x + 1, y, target, seen) or \
            dfs(x - 1, y, target, seen) or \
            dfs(x, y + 1, target, seen) or \
            dfs(x, y - 1, target, seen)
         return dfs(source[0], source[1], target, set()) and
dfs(target[0], target[1], source, set())
ob = Solution()
print(ob.isEscapePossible([[0,1],[1,0]], [0,0], [0,3]))


[[0,1],[1,0]], [0,0], [0,3]



Updated on: 04-Jun-2020


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