find shorttest path

 

def find_shortest_path(maze):
    '''
    maze = [['X', 'X', 'O', 'S', 'X'],
              ['X', 'X', 'O', 'O', 'X'],
              ['X', 'X', 'O', 'X', 'X'],
              ['X', 'X', 'O', 'E', 'X']]'''
    a=[]
    b=[]
    s1=s2=e1=e2=0
    for i in range(len(maze)):
        for j in range(len(maze[0])):
            if maze[i][j]=='S':
                s1=i
                s2=j
            if maze[i][j]=='E':
                e1=i
                e2=j
    a.append([(s1,s2),])
    while len(a)>0:
        b=[]
        for aaa in a:
            #up
            aa=aaa[:]
            if aa[-1][0]-1>=0:
                if aa[-1][0]-1 == e1 and aa[-1][1] == e2:
                    return len(aa)
                if maze[aa[-1][0]-1][aa[-1][1]]=='O' and (aa[-1][0]-1,aa[-1][1]) not in aa:
                    aa.append((aa[-1][0] - 1, aa[-1][1]))
                    b.append(aa)
            #left
            aa=aaa[:]
            if aa[-1][1]-1>=0:
                if aa[-1][0]==e1 and  aa[-1][1]-1==e2:
                    return len(aa)
                if maze[aa[-1][0]][aa[-1][1]-1]=='O' and (aa[-1][0],aa[-1][1]-1) not in aa:
                    aa.append((aa[-1][0], aa[-1][1] - 1))
                    b.append(aa)
            #right
            aa=aaa[:]
            if aa[-1][1]+1