leetcode05 Longest Palindromic Substring 最长回文子串

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本文介绍了一种高效算法来找出给定字符串中的最长回文子串。通过两个示例展示了算法的应用，如输入babad时输出bab或aba，输入cbbd时输出bb。该算法考虑了奇数长度和偶数长度的回文子串。

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Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example:

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Example:

Input: "cbbd"

Output: "bb"

解法：

class Solution:
    # @return a string
    def longestPalindrome(self, s):
        res = ""
        for i in xrange(len(s)):
            # odd case, like "aba"
            tmp = self.helper(s, i, i)
            res = max(tmp,res,key=len)
            # even case, like "abba"
            tmp = self.helper(s, i, i + 1)
            res = max(tmp,res,key=len)

        return res


    def helper(self, s, l, r):
        # 字符的左右都一样
        while l >= 0 and r < len(s) and s[l] == s[r]:
            l -= 1
            r += 1
        return s[l + 1:r]

print Solution().longestPalindrome('abcdcblkjkabcddcbas')