问题描写叙述

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.

解决方式

class Solution {
public:
  bool isPalindrome( string s ) {
    if( s == "" ) {
      return true;
    }
        
    string allAlphanumeric;
    for( int i = 0; i != s.size(); ++i ) {
      if( isalnum( s[i] ) ) {
        allAlphanumeric.push_back( tolower( s[i] ) );
      }
    }
    if( allAlphanumeric.size() == 1 ) {
      return true;
    }

    bool result = true;
    unsigned size = allAlphanumeric.size();
    for( int i = 0; i < size / 2; ++i ) {
      if( allAlphanumeric[i] != allAlphanumeric[size - i - 1] ) {
        result = false;
        break;
      }
    }
    return result;
  }
};