(java)Valid Palindrome

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.

思路:设置两个游标，分别指向串头和串尾，循环比较就行了

代码如下(已通过leetcode)

public class Solution {

public boolean isPalindrome(String s) {

if(s.length()==1) return true;

char[] cs=s.toCharArray();

int i=0,j=cs.length-1;

boolean flag=true;

while(i<j) {

while(i<j&&!Character.isLetterOrDigit(cs[i])){

i++;

}

while(i<j&&!Character.isLetterOrDigit(cs[j])){

j--;

}

char pre=Character.toLowerCase(cs[i]);

char later=Character.toLowerCase(cs[j]);

if(pre==later){

i++;

j--;

} else {

flag=false;

break;

}

}

return flag;

}

}