LeetCode 125. Valid Palindrome

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*

* 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.

*

*

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c++版本 12ms，分析应该是因为重载的s[]操作耗时比c多

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

c版本 4ms，比c++效率高，直接使用指针的效率更高

bool isPalindrome(char* s) {
char *p1 = s, *p2 = s + strlen(s) - 1;
while(p1 < p2){
if(!isalnum(*p1)){p1++;continue;}
if(!isalnum(*p2)){p2--;continue;}
if(tolower(*p1++) != tolower(*p2--)) return false;
}
return true;
}