valid palindrome

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题目:

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:

其实很简单,设置两个指针,头指针i 和尾指针j ,都向中间靠拢,判断有效地 s[i]和s[j]是否相等。不相等则返回false。

class Solution {public:    bool isPalindrome(string s) {        // Start typing your C/C++ solution below        // DO NOT write int main() function                if(s.empty())            return true;        int i=0;        int j=s.size()-1;        while(i<=j)        {            if(!isalnum(s[i]))            {                i++;                continue;            }            if(!isalnum(s[j]))            {                j--;                continue;            }            if(s[i]==s[j])            {                i++;                j--;                continue;            }            else if(isalpha(s[i]) && isalpha(s[j]) && tolower(s[i])==tolower(s[j]))                 {                     i++;                     j--;                     continue;                 }                 else                     return false;        }        return true;    }};
 
Run Status: Accepted!
Program Runtime: 52 milli secs


 

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