064 Minimum Path Sum

class Solution:
    # @param {integer[][]} grid
    # @return {integer}
    def minPathSum(self, grid):
        m = len(grid)
        if m == 0:
            return 0
        n = len(grid[0])
        for i in range(1, m):
            grid[i][0] += grid[i-1][0]
        for j in range(1, n):
            grid[0][j] += grid[0][j-1]
        for i in range(1, m):
            for j in range(1, n):
                grid[i][j] += min(grid[i-1][j], grid[i][j-1])
        return grid[m-1][n-1]