如果字符串或数字颠倒后仍保持不变，则称其为回文。例如，“MADAM”是一个回文字符串，因为即使颠倒过来也会拼写为“MADAM”。但在“LUCKY”的情况下，该字符串不是回文，因为反转后它是“YKCUL”。一些回文数是 365563、48984、12321、171、88、90009、343，一些回文字符串是 MADAM、MALAYALAM、LOL、DAD、MOM、C++&++C 等。 接下来让我们看看回文的逻辑和实现。在本主题中，我们将学习 Java 中的回文。
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为了检查一个数字是否是回文数，可以使用以下算法。
例如，让我们输入数字 353。
353-> temp
Reversednumber: rev=353
如果它们相同，则该数字被称为回文数。
否则，该数字不是回文数。
即
If(inputnum==rev)
{ then palindrome }
Else not palindrome有几种方法可以检查给定的输入数字是否是回文。
让我们详细研究每一个：
代码：
//Java program to check whether a String is a Palindrome or not using For Loop
import java.util.*;
public class PalindromeNumberExample {
//main method
public static void main(String[] args) {
int r=0 ; //reversed Integer
int rem, num; //remainder and original number
Scanner s = new Scanner(System.in);
System.out.print("Enter number that has to be checked:");
num = s.nextInt();
//Store the number in a temporary variable
int temp = num;
//loop to find the reverse of a number
for( ;num != 0; num /= 10 )
{
rem = num % 10; // find the modulus of the number when divided by 10
r = r * 10 + rem;
}
//check whether the original and reversed numbers are equal
if (temp == r)
{
System.out.println(temp + " is input number");
System.out.println(r + " is the reversed number");
System.out.println("Since they are equal " + temp + " is a palindrome number");
}
else
{
System.out.println(temp + " is input number");
System.out.println(r + " is the reversed number");
System.out.println("Since they are not equal " + temp + " is not a palindrome number");
}
}
}输出 1：
这里，由于353颠倒后是一样的，所以被认为是回文。
输出 2：
这里，由于 234 颠倒后仍然不一样，因此不被视为回文。
代码：
//Java program to check whether a number is a Palindrome or not using While Loop
import java.util.*;
public class PalindromeNumberExample {
public static void main(String[] args) {
int r=0, rem, num;
Scanner s = new Scanner(System.in);
System.out.print("Enter number that has to be checked:");
num = s.nextInt();
//Store the number in a temporary variable
int temp = num;
//loop to find the reverse of a number
while( num != 0 )
{
rem= num % 10;
r= r * 10 + rem;
num=num/10;
}
//check whether the original and reversed numbers are equal
if (temp == r)
{
System.out.println(temp + " is input number");
System.out.println(r + " is the reversed number");
System.out.println("Since they are equal " + temp + " is a palindrome number");
}
else
{
System.out.println(temp + " is input number");
System.out.println(r + " is the reversed number");
System.out.println("Since they are not equal " + temp + " is not a palindrome number");
}
}
}输出 1：
输出 2：
代码：
//Java program to check whether a String is a Palindrome or not using Library method
import java.util.*;
public class PalindromeNumberExample {
//Function to check whether the string is palindrome or not
public static void PalindromeCheck(String str)
{
// reverse the input String
String rev = new StringBuffer(str).reverse().toString();
// checks whether the string is palindrome or not
if (str.equals(rev))
{
System.out.println("input string is :" + str);
System.out.println("Reversed string is :" + rev);
System.out.println("Since the input and reversed string are equal, "+ str +" is a palindrome");
}
else
{
System.out.println("input string is :" + str);
System.out.println("Reversed string is :" + rev);
System.out.println("Since the input and reversed string are not equal, "+ str +" is not a palindrome");
}
}
public static void main (String[] args)
{
PalindromeCheck("MALAYALAM");
}
}输出：
这里，输入字符串是在程序本身中传递的。
要检查字符串是否是回文，还可以使用以下程序。
代码：
//Java program to check whether a String is a Palindrome or not
import java.util.*;
public class PalindromeNumberExample {
public static void main(String args[])
{
String st, rev = "";
Scanner sc = new Scanner(System.in);
System.out.println("Enter the string that has to be checked:");
st = sc.nextLine();
int len = st.length(); //length of the string
for ( int i = len- 1; i >= 0; i-- )
rev = rev + st.charAt(i);
if (st.equals(rev))
{
System.out.println("input string is :" + st);
System.out.println("Reversed string is :" + rev);
System.out.println("Since the input and reversed string are equal, "+ st +" is a palindrome");
}
else
{
System.out.println("input string is :" + st);
System.out.println("Reversed string is :" + rev);
System.out.println("Since the input and reversed string are not equal, "+ st +" is not a palindrome");
}
}
}输出：
如果一个数字即使颠倒也保持不变，则称为回文数。回文也可以在字符串中检查。回文数和字符串有 MOM、MALAYALAM、DAD、LOL、232、1331 等。本文档涵盖了回文数的几个方面，如算法、方法、实现等。
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