Python Path Finding with Breadth First Search

The breadth first search algorithm is a very famous algorithm that is used to traverse a tree or graph data structure. It is guaranteed to find the shortest path from a start node to an end node if such path exists. This algorithm can be used for a variety of different tasks but for this example we will use it to solve a maze.

How it Works

For a detailed explanation and walk through please watch the video.

In short the breadth first search algorithm creates a set of all possible routes and attempts each one until it finds the end node. It is a queue based algorithm. It is extremely inefficient and is not ideal for large data structures. Once the algorithm finds a path that reaches the end node it is guaranteed that this is the shortest possible path. This is because of the queue structure that the algorithm uses.

Path Finding With Breadth First Search

One of the common applications of breadth first search is to perform path finding. Typically this is done in a 2D maze. The code below implements the breadth first search algorithm to traverse and find the shortest path out of a maze.

```import queue

def createMaze():
maze = []
maze.append(["#","#", "#", "#", "#", "O","#"])
maze.append(["#"," ", " ", " ", "#", " ","#"])
maze.append(["#"," ", "#", " ", "#", " ","#"])
maze.append(["#"," ", "#", " ", " ", " ","#"])
maze.append(["#"," ", "#", "#", "#", " ","#"])
maze.append(["#"," ", " ", " ", "#", " ","#"])
maze.append(["#","#", "#", "#", "#", "X","#"])

return maze

def createMaze2():
maze = []
maze.append(["#","#", "#", "#", "#", "O", "#", "#", "#"])
maze.append(["#"," ", " ", " ", " ", " ", " ", " ", "#"])
maze.append(["#"," ", "#", "#", " ", "#", "#", " ", "#"])
maze.append(["#"," ", "#", " ", " ", " ", "#", " ", "#"])
maze.append(["#"," ", "#", " ", "#", " ", "#", " ", "#"])
maze.append(["#"," ", "#", " ", "#", " ", "#", " ", "#"])
maze.append(["#"," ", "#", " ", "#", " ", "#", "#", "#"])
maze.append(["#"," ", " ", " ", " ", " ", " ", " ", "#"])
maze.append(["#","#", "#", "#", "#", "#", "#", "X", "#"])

return maze

def printMaze(maze, path=""):
for x, pos in enumerate(maze[0]):
if pos == "O":
start = x

i = start
j = 0
pos = set()
for move in path:
if move == "L":
i -= 1

elif move == "R":
i += 1

elif move == "U":
j -= 1

elif move == "D":
j += 1

for j, row in enumerate(maze):
for i, col in enumerate(row):
if (j, i) in pos:
print("+ ", end="")
else:
print(col + " ", end="")
print()

def valid(maze, moves):
for x, pos in enumerate(maze[0]):
if pos == "O":
start = x

i = start
j = 0
for move in moves:
if move == "L":
i -= 1

elif move == "R":
i += 1

elif move == "U":
j -= 1

elif move == "D":
j += 1

if not(0 <= i < len(maze[0]) and 0 <= j < len(maze)):
return False
elif (maze[j][i] == "#"):
return False

return True

def findEnd(maze, moves):
for x, pos in enumerate(maze[0]):
if pos == "O":
start = x

i = start
j = 0
for move in moves:
if move == "L":
i -= 1

elif move == "R":
i += 1

elif move == "U":
j -= 1

elif move == "D":
j += 1

if maze[j][i] == "X":
print("Found: " + moves)
printMaze(maze, moves)
return True

return False

# MAIN ALGORITHM

nums = queue.Queue()
nums.put("")