712. 两个字符串的最小ASCII删除和

代码：

class Solution:
    def minimumDeleteSum(self, s1: str, s2: str) -> int:

        dp = [[0 for _ in range(len(s2)+1)] for _ in range(len(s1)+1)]

        for i in range(1,len(s1)+1):
            dp[i][0] = dp[i-1][0] + ord(s1[i-1])
        for j in range(1, len(s2)+1):
            dp[0][j] = dp[0][j-1] + ord(s2[j-1])

        for i in range(1, len(s1)+1):
            for j in range(1, len(s2)+1):
                if s1[i-1] == s2[j-1]:
                    dp[i][j] = dp[i-1][j-1]
                else:
                    dp[i][j] = min(dp[i][j-1] + ord(s2[j-1]),
                                   dp[i-1][j] + ord(s1[i-1]))



        return dp[-1][-1]