一开始以为只有字母，结果是数字和字母，挂了好几次。
class Solution {
public boolean isPalindrome(String s) {
int hi = s.length()-1;
int lo = 0 ;
while(lo<=hi)
{
while(lo<=hi&&!isAlphanumeric(s.charAt(lo)))
lo++;
while(hi>=lo&&!isAlphanumeric(s.charAt(hi)))
hi--;
if(hi==lo-1)
return true;
char ch1 = Character.toLowerCase(s.charAt(lo));
char ch2 = Character.toLowerCase(s.charAt(hi));
if(ch1!=ch2) return false;
hi--;
lo++;
}
return true;
}
private boolean isAlphanumeric (char ch)
{
return (ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z')||(ch>='0'&&ch<='9');
}
}
