[Leetcode][python]Interleaving String/交错字符串

dp[i][j] = (dp[i-1][j] and s1[i-1]==s3[i+j-1]) or (dp[i][j-1] and s2[j-1]==s3[i+j-1])

class Solution(object):
    def isInterleave(self, s1, s2, s3):
        """
        :type s1: str
        :type s2: str
        :type s3: str
        :rtype: bool
        """
        if len(s1)+len(s2)!=len(s3): 
            return False
        dp=[[False for i in range(len(s2)+1)] for j in range(len(s1)+1)]
        dp[0][0]=True
        for i in range(1, len(s1)+1):
            dp[i][0] = dp[i-1][0] and s3[i-1]==s1[i-1]  # 边界：之前需要符合并且s1和s3对应位置相同
        for i in range(1, len(s2)+1):
            dp[0][i] = dp[0][i-1] and s3[i-1]==s2[i-1]  # 边界：之前需要符合并且s1和s3对应位置相同
        for i in range(1, len(s1)+1):
            for j in range(1, len(s2)+1):
                # print i, j, s1[i-1], s3[i+j-1], s2[j-1], s3[i+j-1]
                dp[i][j] = (dp[i-1][j] and s1[i-1]==s3[i+j-1]) or (dp[i][j-1] and s2[j-1]==s3[i+j-1])

        # for i in range(len(s1)+1):
        #     print dp[i]

        return dp[-1][-1]