Leetcode Valid Palindrome

Valid Palindrome

 Total Accepted: 6669 Total Submissions: 31102My Submissions

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.

很简单的题目： 2星级。

考点：

1 会判断是否是字母和数字

2 知道什么是Palindrome

可以利用函数库判断是否为数字或者字母，程序如下：

bool isPalindrome(string s) {for (int i = 0, j = s.size()-1; i < j; i++, j--){while (i<j && (!isalpha(s[i]) && !isdigit(s[i]))) i++;while (i<j && (!isalpha(s[j]) && !isdigit(s[j]))) j--;if (i<j && tolower(s[i]) != tolower(s[j])) return false;}return true;}

自家写函数判断也很简单：

bool isPalindrome(string s) {for (int i = 0, j = s.size()-1; i < j; i++, j--){while (s[i] && (!isTestChar(s[i]))) i++;while (s[j] && (!isTestChar(s[j]))) j--;if (i<j && !isEqual(s[i], s[j])) return false;}return true;}bool isTestChar(char a){int i = a;return (i>=97 && i<=122) || (i>=65 && i<=90) || (i>=48 && i<=57);}bool isEqual(char a, char b){return a == b || int(a) == int(b)-32 || int(b) == int(a)-32;}/*char a = 'A';//65a = 'a';//97a = 'Z';//90a = 'z';//122a = '1';//49a = '0';//48*/

//2014-2-18 updatebool isPalindrome(string s) {for (int i = 0, j = s.length()-1; i < j; ){if (isalnum(s[i]) && isalnum(s[j])){if (tolower(s[i]) != tolower(s[j])) return false;i++, j--;}if (i<j && !isalnum(s[i])) i++;if (i<j && !isalnum(s[j])) j--;}return true;}