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.
需要注意点：
1）empty string问题(不能用while(!chacter[left]) left++)而要用if(!chacter[left]){left++ continue}
2)大小写字母的转换，注意0~9系统是认识的。
class Solution {
public:
bool isCharacter(char c)
{
if((c >= ‘a‘&&c <= ‘z‘)||(c >= ‘A‘ && c <= ‘Z‘)||(c >= ‘0‘&&c <= ‘9‘))
return true;
else
return false;
}
char Turntosmallalpha(char c)
{
if(c >= ‘A‘&&c <= ‘Z‘)
c = c + ‘a‘ - ‘A‘;
return c;
}
bool isPalindrome(string s) {
int left = 0;
int right = s.size() - 1;
bool flg = true;
while(left <= right)
{
if(!isCharacter(s[left]))
{
left ++;
continue;
}
if(!isCharacter(s[right]))
{
right --;
continue;
}
if(Turntosmallalpha(s[left]) != Turntosmallalpha(s[right]))
{
flg = false;
break;
}
left ++;
right --;
}
return flg;
}
};