python leetcode 62. Unique Paths

典型的DP题目，这一刻的路径步数与上一时刻的路径步数相关。

class Solution(object):
    def uniquePaths(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        dp=[[0]*m for i in range(n)]
        for i in range(m):
            dp[0][i] = 1 
        for j in range(n):
            dp[j][0] = 1 
        for i in range(1,n):
            for j in range(1,m):
                dp[i][j] = dp[i-1][j] + dp[i][j-1]
        return dp[n-1][m-1]