64. Minimum Path Sum

class Solution:
    def minPathSum(self, grid: List[List[int]]) -> int:
        #f[i][j] = min(f[i][j-1], f[i-1][j]) + grid[i][j]
        if not grid:
            return None
        m = len(grid)
        n = len(grid[0])
        path = [0] * n
        path[0] = grid[0][0]
        for i in range(1, n):
            path[i] = path[i-1] + grid[0][i]
        for i in range(1, m):
            for j in range(n):
                if j == 0:
                    path[j] = path[j] + grid[i][j]
                else:
                    path[j] = min(path[j], path[j-1]) + grid[i][j]
        return path[-1]

class Solution:
    def minPathSum(self, grid: List[List[int]]) -> int:
        #f[i][j] = min(f[i][j-1], f[i-1][j]) + grid[i][j]
        if not grid:
            return None
        m = len(grid)
        n = len(grid[0])
        f = [[float("inf")] * (n + 1) for _ in range(m + 1)]
        f[0][1] = 0
        for i in range(1, m + 1):
            for j in range(1, n + 1):
                f[i][j] = min(f[i][j-1], f[i-1][j]) + grid[i-1][j-1]
        return f[-1][-1]