下降路径最小和

思路：
新建一个跟数组一样大的dp表，dp[i][j]表示经过A[i][j]点时最小的路径和。

class Solution(object):
    def minFallingPathSum(self, A):
        """
        :type A: List[List[int]]
        :rtype: int
        """
        m = len(A)
        n = len(A[0])
        dp = [[0] * n for _ in range(m)]
        dp[0] = A[0]
        for i in range(1, m):
            for j in range(n):
                if 0<=j-1<=n-1 and 0<=j+1<=n-1:
                    dp[i][j] = min(dp[i-1][j], dp[i-1][j-1], dp[i-1][j+1]) + A[i][j]
                elif 0<=j-1<=n-1:
                    dp[i][j] = min(dp[i-1][j], dp[i-1][j-1]) + A[i][j]
                else:
                    dp[i][j] = min(dp[i-1][j], dp[i-1][j+1]) + A[i][j]
        return min(dp[-1])