valid-palindrome leetcode C++
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.
C++
class Solution {
bool isAlphaNum(char &ch) {
if (ch >= 'a' && ch <= 'z') return true;
if (ch >= 'A' && ch <= 'Z') return true;
if (ch >= '0' && ch <= '9') return true;
return false;
}
public:
bool isPalindrome(string s) {
int left = 0, right = s.size() - 1 ;
while (left < right) {
if (!isAlphaNum(s[left])) ++left;
else if (!isAlphaNum(s[right])) --right;
else if ((s[left] + 32 - 'a') %32 != (s[right] + 32 - 'a') % 32) return false;
else {
++left; --right;
}
}
return true;
}
bool isPalindrome2(string s){
if("" == s) return true;
int left = 0;
int right = s.size() - 1;
while (left<right){
if(!isAlphaNum(s[left])) left++;
else if (!isAlphaNum(s[right])) right--;
else if ((s[left] + 32 - 'a') %32 != (s[right] + 32 - 'a') % 32) return false;
else { left++; right--;}
}
return true;
}
};
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