一个4x4的矩阵，从左上到右下走，可以左右上下走，但是不能走走过的点，有多少种走法？

4x4.py

gCnt = 0 
def main():

    squre = []
    for i in range(4):
        squre.append([0,0,0,0])
    print squre
    
    
    def dfs(x,y,d):
        if (x==3 and y==3) :
            global gCnt
            gCnt = gCnt+1
            print 'found ', gCnt 
            return
    
        squre[x][y] = d
        
        for delta in [[0,1],[0,-1],[1,0],[-1,0]]:
            xx = x + delta[0]
            yy = y + delta[1]
            
            if (xx<0 or xx>=4):continue
            if (yy<0 or yy>=4):continue
            if (squre[xx][yy]): continue
            dfs(xx,yy,d+1)
        squre[x][y] = 0
    
    dfs(0,0,1)
    

main()