[Leetcode]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.

判断字符串s3是否能由字符串s1和s2交织组成~可以用动态规划来解~动态规划的题只要能想出递推公式来，就很直观了~在这儿用dp[i][j]来表示是否能用s1的前i个字符和s2的前j个字符来表示s3的前i + j 个字符~下面代码是二维动态规划，还可以简化成一维动态规划，具体可以参考 http://blog.youkuaiyun.com/linhuanmars/article/details/24683159

class Solution:
    # @return a boolean
    def isInterleave(self, s1, s2, s3):
        if len(s3) != len(s1) + len(s2): return False
        dp = [[False for i in xrange(len(s2) + 1)] for j in xrange(len(s1) + 1)]
        for i in xrange(len(s1) + 1):
            for j in xrange(len(s2) + 1):
                if i == 0 and j == 0: dp[i][j] = True
                elif i == 0: dp[i][j] = s2[:j] == s3[:j]
                elif j == 0: dp[i][j] = s1[:i] == s3[:i]
                else:
                    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])
        return dp[len(s1)][len(s2)]