Leetcode-Valid Palindrome

#Leetcode

题目描述

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.

思路

双指针,扫描。需要用到一些库函数。

AC代码

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;

bool isPalindrome(string s)
{
    	int n = s.length();
    	int left = 0, right = n - 1;
    	//tolower把字符转换成小写字母,非字母字符不做出处理
    	//isalnum(c) c为数字0-9或字母a-z及A-Z时,返回非零值,否则返回零。
    	while(left <= right)
    	{
    		while(left <= right && !isalnum(s[left]))
    			left++;
    		while(left <= right && !isalnum(s[right]))
    			right--;
    		if(left > right)
    			break;
    		if(isdigit(s[left]) && s[left] != s[right])
    			return false;
    		if(tolower(s[left]) != tolower(s[right]))
    			return false;
    		left++;
    		right--;
    	}
    	return true;
}

int main()
{
    	string s;
    
    #ifndef ok
    	freopen("in1.in","r",stdin);
    	freopen("std1.out","w",stdout);
    #endif
    
    	while(getline(cin,s,'\n'))
    	{
    		if(isPalindrome(s))
    			cout<<"true"<<endl;
    		else
    			cout<<"false"<<endl;
    	}
    	
    #ifndef ok
    	fclose(stdin);
    	fclose(stdout);
    #endif
    
    	return 0;
}