basic programming python: Python-based recursive algorithm implementation issues Maze

This paper describes examples of problems Maze Python recursive algorithm implemented. Share to you for your reference, as follows:

What is recursion?

Simple to understand is the function that calls itself the process is called recursion.

When to use recursion?

If a problem can be expressed as iteration smaller scale, you can use a recursive algorithm.
Maze: a two-dimensional array consisting of 0 or 1, 1 is assumed to move to the point, it is 0 can not move to the point, how to proceed from a point intermediate the array value is 1, only upward and downward each four directions moving a unit, when moving to the edge of a two-dimensional array, the solution of the problem can be obtained, similar problems can be referred to as a maze.

You can use a nested list represents a two-dimensional array in python. [3] [3] Assuming maze starting a 6 * 6, the question from the array coordinates, can not judge the success of the maze.

maze=[[1,0,0,1,0,1],
   [1,1,1,0,1,0],
   [0,0,1,0,1,0],
   [0,1,1,1,0,0],
   [0,0,0,1,0,0],
   [1,0,0,0,0,0]]

For this maze, we can use the idea of ​​recursive good solution. For a dot array, four directions of the point can be easily represented, whenever a movable point of time to move the whole issue has become a problem as the initial state and by adding or subtracting the horizontal and vertical coordinates, the search continues four directions can be moved to find a point, move to the edge of the array known.

So we can code:

# 判断坐标的有效性，如果超出数组边界或是不满足值为1的条件，说明该点无效返回False，否则返回True。
def valid(maze,x,y):
  if (x>=0 and x<len(maze) and y>=0 and y<len(maze[0]) and maze[x][y]==1):
    return True
  else:
    return False
# 移步函数实现
def walk(maze,x,y):
  # 如果位置是迷宫的出口，说明成功走出迷宫
  if(x==0 and y==0):
    print("successful!")
    return True
  # 递归主体实现
  if valid(maze,x,y):
    # print(x,y)
    maze[x][y]=2 # 做标记，防止折回
    # 针对四个方向依次试探，如果失败，撤销一步
    if not walk(maze,x-1,y):
      maze[x][y]=1
    elif not walk(maze,x,y-1):
      maze[x][y]=1
    elif not walk(maze,x+1,y):
      maze[x][y]=1
    elif not walk(maze,x,y+1):
      maze[x][y]=1
    else:
      return False # 无路可走说明，没有解 
  return True
walk(maze,3,3)

Recursion is a good thing ah!
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