【*E】leetcode-125.验证回文串

package com.leetcode.easy;
 
public class Hot125_isPalindrome {
	
	/**
	 * 调用reverse
	 * @description:
	 * @date:2022年6月28日
	 * @param s
	 * @return
	 */
	public static boolean isPalindrome(String s) {
		StringBuilder sb = new StringBuilder();
		int length = s.length();
		for(int i = 0;i<length; ++i) {
			char ch = s.charAt(i);
			if(Character.isLetterOrDigit(ch)){
				sb.append(Character.toLowerCase(ch));
			}
		}
		StringBuilder sbRev = new StringBuilder(sb).reverse();
		
		return sb.toString().equals(sbRev.toString());
    }
	
	/**
	 * 左右指针
	 * @description:
	 * @date:2022年6月28日
	 * @param s
	 * @return
	 */
	public static boolean isPalindrome2(String s) {
		StringBuilder sb = new StringBuilder();
		int length = s.length();
		for(int i = 0;i< length;++i) {
			char ch = s.charAt(i);
			if(Character.isLetterOrDigit(ch)) {
				sb.append(Character.toLowerCase(ch));
			}
		}
		
		int n = sb.length();
		int left = 0, right = n - 1;
		while(left < right) {
			if(sb.charAt(left) != sb.charAt(right)) {
				return false;
			}
			++left;
			--right;
		}
		return true;
	}
	
	/**
	 * 在原串上判断
	 * @description:
	 * @date:2022年6月28日
	 * @param s
	 * @return
	 */
	public static boolean isPalindrome3(String s) {
		int n = s.length();
		int left = 0, right = n-1;
		s = s.toLowerCase();
		while(left < right) {
			while(left < right && !Character.isLetterOrDigit(s.charAt(left)))
				++left;
			while(left < right && !Character.isLetterOrDigit(s.charAt(right)))
				--right;
			if(left < right) {
				if(s.charAt(left) != s.charAt(right))
					return false;
				++left;
				--right;
			}
		}
		return true;
	}
	
	
	//------------------for-test-------------
	public static void main(String[] args) {
		String s = "A man, a plan, a canal: Panama";
		System.out.println(isPalindrome(s));
		System.out.println(isPalindrome2(s));
		System.out.println(isPalindrome3(s));
	}
}