判断字符串是否为回文 python实现

题目：判断一个字符串是否是回文

方法：设定两个指针，分别有头尾向中间移动 或者由中间向两边移动

#!/usr/bin/env python
# -*- coding: utf-8 -*-

def isPalindrome(s):
	'''判断一个字符串是否为回文'''
	lens = len(s)
	if lens <=1:
		return True
	l,r = 0, lens-1
	while l<r:
		if s[l] != s[r]:
			return False
		l += 1
		r -= 1
	return True

def longestPalindrome(s):
	'''查找一个字符串中的最长回文字串'''
	maxl, lens = 1, len(s)
	for i in xrange(lens):
		j = 1
		while i-j>=0 and i+j<lens:
			if s[i-j] != s[i+j]:
				break
			j += 1
		if 2*(j-1)+1 > maxl:
			maxl = 2*(j-1) + 1
		j = 0
		while i-j>=0 and i+j+1<lens:
			if s[i-j] != s[i+j+1]:
				break
			j += 1
		if 2*(j-1)+2 > maxl:
			maxl = 2*(j-1) + 2
	return maxl
		

if __name__ == '__main__':
	s = 'qabcdefgfedcbaa'
	print isPalindrome(s)
	print longestPalindrome(s)