动态规划--最小路径和

题目描述
给定一个由非负整数填充的m x n的二维数组，现在要从二维数组的左上角走到右下角，请找出路径上的所有数字之和最小的路径。
注意：你每次只能向下或向右移动。

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.
Note: You can only move either down or right at any point in time.

class Solution:
    def minPathSum(self , grid ):
        m=len(grid)
        n=len(grid[0])
        # write code here
        res=[[0 for i in range(n)] for i in range(m)]
        
        for i in range(m):
            for j in range(n):
                if i==0:
                    res[0][j]=grid[0][j]+res[0][j-1]
                elif j==0:
                    res[i][0]=grid[i][0]+res[i-1][0]
                else:
                    res[i][j]=grid[i][j]+self.mini(res[i-1][j],res[i][j-1])
        return res[i][j]
    def mini(self,a,b):
        return a if a<b else b
        return a<b and a or b