leetcode/code/lc125.java at master · mJackie/leetcode · GitHub

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package code;

* 125. Valid Palindrome

* 题意：判断是否为回文

* 难度：Easy

* 分类：Two Pointers, String

* 思路：两个指针。另一种是正则表达式替换数字，字母为空格，再反转，判断是否相等。

* Tips：记下另一种方法。第一种方法Bingo!

* lc5, lc9, lc125, lc131, lc234, lc647

public class lc125 {

public static void main(String[] args) {

System.out.println(isPalindrome("A man, a plan, a canal: Panama"));

}

public static boolean isPalindrome(String s) {

int begin = 0;

int end = s.length()-1;

s = s.toLowerCase(); //转为小写

while(begin<end && !(helper(s.charAt(begin)))) begin++;

while(begin<end && !(helper(s.charAt(end)))) end--;

while(begin<end){

if(s.charAt(begin)==s.charAt(end)){

begin++;

end--;

while(begin<end && !(helper(s.charAt(begin)))) begin++;

while(begin<end && !(helper(s.charAt(end)))) end--;

}else{

return false;

}

return true;

}

public static boolean helper(Character ch){ //过滤非字符数字

if(Character.isAlphabetic(ch)||Character.isDigit(ch)) return true;

return false;

}

public boolean isPalindrome2(String s) {

String actual = s.replaceAll("[^A-Za-z0-9]", "").toLowerCase();

String rev = new StringBuffer(actual).reverse().toString();

return actual.equals(rev);

}

leetcode/code/lc125.java at master · mJackie/leetcode · GitHub

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