Leetcode: 489. Robot Room Cleaner

Mistake: Incorrect evaluation of solution's viability. My first idea was to make a Depth-first search, but spent much of the time thinking about other ways to do the search.

# """
# This is the robot's control interface.
# You should not implement it, or speculate about its implementation
# """
#class Robot:
#    def move(self):
#        """
#        Returns true if the cell in front is open and robot moves into the cell.
#        Returns false if the cell in front is blocked and robot stays in the current cell.
#        :rtype bool
#        """
#
#    def turnLeft(self):
#        """
#        Robot will stay in the same cell after calling turnLeft/turnRight.
#        Each turn will be 90 degrees.
#        :rtype void
#        """
#
#    def turnRight(self):
#        """
#        Robot will stay in the same cell after calling turnLeft/turnRight.
#        Each turn will be 90 degrees.
#        :rtype void
#        """
#
#    def clean(self):
#        """
#        Clean the current cell.
#        :rtype void
#        """

class Solution:
    def cleanRoom(self, robot):
        """
        :type robot: Robot
        :rtype: None
        """

        DIR = [[-1, +0], [+0, -1], [+1, +0], [+0, +1]]

        seen = set()
        def dfs(i, j, d):
            if (i, j, d) in seen:
                return
            robot.clean()
            seen.add((i, j, d))

            if robot.move():
                dfs(i + DIR[d][0], j + DIR[d][1], d)
                robot.turnLeft()
                robot.turnLeft()
                robot.move()
                robot.turnLeft()
                robot.turnLeft()

            for k in range(3):
                robot.turnLeft()
                dfs(i, j, (d + k + 1) % len(DIR))
            robot.turnLeft()

        dfs(0, 0, 0)