leetcode 1616. Split Two Strings to Make Palindrome （python）

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描述

You are given two strings a and b of the same length. Choose an index and split both strings at the same index, splitting a into two strings: a_prefix and a_suffix where a = a_prefix + a_suffix, and splitting b into two strings: b_prefix and b_suffix where b = b_prefix + b_suffix. Check if a_prefix + b_suffix or b_prefix + a_suffix forms a palindrome.

When you split a string s into s_prefix and s_suffix, either s_suffix or s_prefix is allowed to be empty. For example, if s = "abc", then "" + "abc", "a" + "bc", "ab" + "c" , and "abc" + "" are valid splits.

Return true if it is possible to form a palindrome string, otherwise return false.

Notice that x + y denotes the concatenation of strings x and y.

Example 1:

• Input: a = "x", b = "y"
• Output: true
• Explaination: If either a or b are palindromes the answer is true since you can split in the following way:
• a_prefix = "", a_suffix = "x"
• b_prefix = "", b_suffix = "y"
• Then, a_prefix + b_suffix = "" + "y" = "y", which is a palindrome.

Example 2:

• Input: a = "abdef", b = "fecab"
• Output: true

Example 3:

• Input: a = "ulacfd", b = "jizalu"

• Output: true

• Explaination: Split them at index 3:

• a_prefix = "ula", a_suffix = "cfd"

• b_prefix = "jiz", b_suffix = "alu"

• Then, a_prefix + b_suffix = "ula" + "alu" = "ulaalu", which is a palindrome.

Example 4:

• Input: a = "xbdef", b = "xecab"
• Output: false

Note:

1 <= a.length, b.length <= 10^5
a.length == b.length
a and b consist of lowercase English letters
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解析

根据题意，给定两个长度相同的字符串 a 和 b。 选择一个索引并在同一索引处拆分两个字符串，将 a 拆分为两个字符串：a_prefix 和 a_suffix，其中 a = a_prefix + a_suffix，将 b 拆分为两个字符串：b_prefix 和 b_suffix，其中 b = b_prefix + b_suffix。 检查 a_prefix + b_suffix 或 b_prefix + a_suffix 是否形成回文。

将字符串 s 拆分为 s_prefix 和 s_suffix 时，允许 s_suffix 或 s_prefix 为空。 例如，如果 s = "abc"，则 "" + "abc"、"a" + "bc"、"ab" + "c" 和 "abc" + "" 是有效的拆分。如果可以形成回文字符串则返回 True ，否则返回 False。请注意，x + y 表示字符串 x 和 y 的串联。

其实这道题使用贪心的思想还是比较容易的，加入我们有两个字符串 a 和 b ，并且用中线假定划分的位置，如下：

• a：AB | CD | EF
• b：GH | KJ | LM

如果 a 的前缀和 b 的后缀能组成回文，那么 AB 一定和 LM 能组成回文，那么只需要判断并且 CD 或者 KJ 是否是回文即可，即：AB+CD+LM 或者 AB+KJ+LM 这两种情况可以组成回文。将 b 的前缀和 a 的后缀组成回文也是相同的逻辑。

解答

class Solution(object):
    def checkPalindromeFormation(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: bool
        """
        return self.check(a, b) or self.check(b,a)
    
    def check(self, a, b):
        if len(a) == 1 : return True
        i = 0
        j = len(a) - 1
        while i<=j and a[i]==b[j]:
            i+=1
            j-=1
        if i>j:return True
        return self.isPalindrome(a[i:j+1]) or self.isPalindrome(b[i:j+1])
    
    def isPalindrome(self, s):
        i = 0
        j = len(s)-1
        while i<=j and s[i]==s[j]:
            i+=1
            j-=1
        return i>j
        

        	      
		
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运行结果

Runtime: 119 ms, faster than 66.67% of Python online submissions for Split Two Strings to Make Palindrome.
Memory Usage: 15.6 MB, less than 38.10% of Python online submissions for Split Two Strings to Make Palindrome.
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原题链接：leetcode.com/problems/sp…

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