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

Example 1:

Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbcbcac"
Output: true

Example 2:

Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbbaccc"
Output: false

Answer:

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
        
        dp=[[False]*(l1+2) for _ in range(l2+2)]
        
        dp[0][0]=True
        
        for i in range(1,l1+1):
            if s3[i-1]==s1[i-1]:
                dp[0][i]=dp[0][i-1]
            else:
                break
                
        for i in range(1,l2+1):
            if s3[i-1]==s2[i-1]:
                dp[i][0]=dp[i-1][0]
            else:
                break
        
     
        
        for i in range(1,l2+1):
            for j in range(1,l1+1):
                if s3[i+j-1]==s1[j-1]:
                    dp[i][j]=dp[i][j] or dp[i][j-1]
                if s3[i+j-1]==s2[i-1]:
                    dp[i][j]=dp[i][j] or dp[i-1][j]
        return dp[l2][l1]