leetcode [64] 最小路径和

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给定一个包含非负整数的 m x n 网格，请找出一条从左上角到右下角的路径，使得路径上的数字总和为最小。

说明：每次只能向下或者向右移动一步。

示例:

输入:
[
  [1,3,1],
  [1,5,1],
  [4,2,1]
]
输出: 7
解释: 因为路径 1→3→1→1→1 的总和最小。

class Solution:
    def minPathSum(self, grid: List[List[int]]) -> int:
        if len(grid) == 0 or len(grid[0]) == 0:
            return 0
        if len(grid) == 1 or len(grid[0]) == 1:
            return sum(sum(g) for g in grid)
        
        for i in range(1, len(grid)):
            grid[i][0] += grid[i - 1][0]
        for i in range(1, len(grid[0])):
            grid[0][i] += grid[0][i - 1]
        for i in range(1, len(grid)):
            for j in range(1, len(grid[0])):
                grid[i][j] += min(grid[i][j - 1], grid[i - 1][j])
        return grid[-1][-1]