动态规划

grid[i][j] 表示从左上角开始 走到 i j 位置的最小路径和

1. 第一列 依次相加
2. 第一行 依次相加
3. 当 i > 1 and j > 1时 grid[i][j] += min(grid[i - 1][j], grid[i][j - 1])

class Solution:
    def minPathSum(self, grid: List[List[int]]) -> int:
        
        # 动态规划
        
        m = len(grid)
        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]