java字符串练习题7、验证回文串

package com.item.actoin;

import java.util.Scanner;

public class Demo {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.nextLine();
		sc.close();
		//正向
		StringBuffer sb = new StringBuffer();
        int length = s.length();
        for (int i = 0; i < length; i++) {
            char ch = s.charAt(i);
            //判断ch是否为字母或数字·这里直接排除了其它符号和空格
            if (Character.isLetterOrDigit(ch)) {
            	//小写处理，然然后累计在一起
                sb.append(Character.toLowerCase(ch));
            }
        }
        //反向
        StringBuffer rev = new StringBuffer(sb).reverse();
		System.out.println(sb.toString().equals(rev.toString()));
	}
}

package com.item.actoin;

import java.util.Scanner;

public class Demo {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.nextLine();
		sc.close();
		//返回的结果
		boolean result = true;
		//使用StringBuffer效率高一些
		StringBuffer sb = new StringBuffer();
		int length = s.length();
		for (int i = 0; i < length; i++) {
			char ch = s.charAt(i);
			//只要字母和数字
			if (Character.isLetterOrDigit(ch)) {
				//存储字母和数字
				sb.append(Character.toLowerCase(ch));
			}
		}
		int n = sb.length();
		//左右一起处理，这种方法叫做双指针，也叫一个不jia太bi礼fa貌的数学词语。
		int left = 0, right = n - 1;
		//左右相互判断，只要有1个不相同就直接返回false;
		while (left < right) {
			if (Character.toLowerCase(sb.charAt(left)) != Character.toLowerCase(sb.charAt(right))) {
				result = false;
				break;
			}
			++left;
			--right;
		}
		System.out.println(result);
	}
}