114. Unique Paths

class Solution:    """    @param: m: positive integer (1 <= m <= 100)    @param: n: positive integer (1 <= n <= 100)    @return: An integer    """    def uniquePaths(self, m, n):        # write your code here        f=[[0]*n]*m        for i in range(n):            f[0][i]=1        for i in range(m):            f[i][0]=1        for i in range(1,m):            for j in range(1,n):                f[i][j]=f[i][j-1]+f[i][j]        return f[m-1][n-1]