97. Interleaving String

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 = "aabcc",
s2 = "dbbca",

When s3 = "aadbbcbcac", return true.
When s3 = "aadbbbaccc", return false.

class Solution(object):    def isInterleave(self, s1, s2, s3):        """        :type s1: str        :type s2: str        :type s3: str        :rtype: bool        """        len_s1 = len(s1)        len_s2 = len(s2)        len_s3 = len(s3)        if len_s1 + len_s2 != len_s3:            return False        is_inter_leave = [[True for i in xrange(len_s1+1)] for j in xrange(len_s2+1)]        for i in xrange(1,len_s1+1):            is_inter_leave[0][i] = is_inter_leave[0][i-1] and s1[i-1] == s3[i-1]        for j in xrange(1,len_s2+1):            is_inter_leave[j][0] = is_inter_leave[j-1][0] and s2[j-1] == s3[j-1]        for i in xrange(1,len_s2+1):            for j in xrange(1,len_s1+1):                is_inter_leave[i][j] = (is_inter_leave[i-1][j] and s2[i-1] == s3[i+j-1]) or (is_inter_leave[i][j-1] and s1[j-1] == s3[i+j-1])                        return is_inter_leave[len_s2][len_s1]