程序代码：

next=[[0,1],[1,0],[0,-1],[-1,0]]
m=3
n=3
book=[range(0,4),range(0,4)]
for i in range(0,4):
    for j in range(0,4):
        book[i][j]=0
map=[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,1]]
def dfs(x,y,step):
    if(x==m,y==n):
        if(step<min):
            min=step

    for k in range(0,4):
        tx=x+next[k][0]
        ty=y+next[k][1]
        if(tx>=0&ty>=0&tx<4&ty<4):
            if(map[tx][ty]!=1&book[tx][ty]==0):
                book[tx][ty]=1
                dfs(tx,ty,step+1)
                book[tx][ty]=0

dfs(0,0,1)

book=[[0 for i in range(4)] for j in range(4)]

def dfs(x,y,step):
    global min
    if x==m and y==n and step<min :
        min=step