class Solution(object):
    def isInterleave(self, s1, s2, s3):
        """
        :type s1: str
        :type s2: str
        :type s3: str
        :rtype: bool
        """
        l1=len(s1)
        l2=len(s2)
        l3=len(s3)
        if (l1+l2)!=l3: return False
        if l1==0 :return s2==s3
        if l2==0 :return s1==s3
        d=[[False for j in xrange(l2+1)]for i in xrange(l1+1)]
        d[0][0]=True
        for i in xrange(1,l1+1):
            if s3[:i]==s1[:i]:
                d[i][0]=True
        for j in xrange(1,l2+1):
            if s3[:j]==s2[:j]:
                d[0][j]=True
        
        for i in xrange(1,l1+1):
            for j in xrange(1,l2+1):
                d[i][j]=(d[i-1][j] and s3[i+j-1]==s1[i-1])or (d[i][j-1] and s3[i+j-1]==s2[j-1])
        return d[l1][l2]