Valid Palindrome

描述

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,

"A man, a plan, a canal: Panama" is a palindrome."race a car" is not a palindrome.

Note:Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

分析

无

代码

  1. // Valid Palindrome
  2. // 时间复杂度O(n)，空间复杂度O(1)
  3. class Solution {
  4. public:
  5.     bool isPalindrome(string s) {
  6.         transform(s.begin(), s.end(), s.begin(), ::tolower);
  7.         auto left = s.begin(), right = prev(s.end());
  8.         while (left < right) {
  9.             if (!::isalnum(*left))  ++left;
  10.             else if (!::isalnum(*right)) --right;
  11.             else if (*left != *right) return false;
  12.             else { left++, right--; }
  13.         }
  14.         return true;
  15.     }
  16. };

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原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/string/valid-palindrome.html