查找给定数字的所有回文数

给定一个整数D ，任务是找到所有D位回文数。

例子：

Input: D = 1
Output: 1 2 3 4 5 6 7 8 9

Input: D = 2
Output: 11 22 33 44 55 66 77 88 99

方法：带D位的数字从10 ^{(D – 1)}到10 ^D – 1开始。因此，从此间隔开始检查每个数字是否是回文。

下面是上述方法的实现：

C++

// C++ implementation of the approach
#include 
using namespace std;
  
// Function to return the
// reverse of num
int reverse(int num)
{
    int rev = 0;
    while (num > 0) {
        rev = rev * 10 + num % 10;
        num = num / 10;
    }
    return rev;
}
  
// Function that returns true
// if num is palindrome
bool isPalindrome(int num)
{
  
    // If the number is equal to the
    // reverse of it then it
    // is a palindrome
    if (num == reverse(num))
        return true;
  
    return false;
}
  
// Function to print all the
// d-digit palindrome numbers
void printPalindromes(int d)
{
    if (d <= 0)
        return;
  
    // Smallest and the largest d-digit numbers
    int smallest = pow(10, d - 1);
    int largest = pow(10, d) - 1;
  
    // Starting from the smallest d-digit
    // number till the largest
    for (int i = smallest;
         i <= largest; i++) {
  
        // If the current number
        // is palindrome
        if (isPalindrome(i))
            cout << i << " ";
    }
}
  
// Driver code
int main()
{
    int d = 2;
  
    printPalindromes(d);
  
    return 0;
}

Java

// Java implementation of the approach 
class GFG 
{
      
    // Function to return the 
    // reverse of num 
    static int reverse(int num) 
    { 
        int rev = 0; 
        while (num > 0) 
        { 
            rev = rev * 10 + num % 10; 
            num = num / 10; 
        } 
        return rev; 
    } 
      
    // Function that returns true 
    // if num is palindrome 
    static boolean isPalindrome(int num) 
    { 
      
        // If the number is equal to the 
        // reverse of it then it 
        // is a palindrome 
        if (num == reverse(num)) 
            return true; 
      
        return false; 
    } 
      
    // Function to print all the 
    // d-digit palindrome numbers 
    static void printPalindromes(int d) 
    { 
        if (d <= 0) 
            return; 
      
        // Smallest and the largest d-digit numbers 
        int smallest = (int)Math.pow(10, d - 1); 
        int largest = (int)Math.pow(10, d) - 1; 
      
        // Starting from the smallest d-digit 
        // number till the largest 
        for (int i = smallest; i <= largest; i++)
        { 
  
            // If the current number 
            // is palindrome 
            if (isPalindrome(i)) 
                System.out.print(i + " "); 
        } 
    } 
      
    // Driver code 
    public static void main (String[] args)
    { 
        int d = 2; 
      
        printPalindromes(d); 
    } 
}
  
// This code is contributed by AnkitRai01

Python3

# Python implementation of the approach
  
# Function to return the
# reverse of num
def reverse(num):
    rev = 0;
    while (num > 0):
        rev = rev * 10 + num % 10;
        num = num // 10;
  
    return rev;
  
# Function that returns true
# if num is palindrome
def isPalindrome(num): 
    # If the number is equal to the
    # reverse of it then it
    # is a palindrome
    if (num == reverse(num)):
        return True;
  
    return False;
  
# Function to prall the
# d-digit palindrome numbers
def printPalindromes(d):
  
    if (d <= 0):
        return;
  
    # Smallest and the largest d-digit numbers
    smallest = pow(10, d - 1);
    largest = pow(10, d) - 1;
  
    # Starting from the smallest d-digit
    # number till the largest
    for i in range(smallest, largest + 1):
  
        # If the current number
        # is palindrome
        if (isPalindrome(i)):
            print(i, end = " ");
  
# Driver code
d = 2;
  
printPalindromes(d);
  
# This code is contributed by 29AjayKumar

C#

// C# implementation of the approach
using System;
      
class GFG 
{
      
    // Function to return the 
    // reverse of num 
    static int reverse(int num) 
    { 
        int rev = 0; 
        while (num > 0) 
        { 
            rev = rev * 10 + num % 10; 
            num = num / 10; 
        } 
        return rev; 
    } 
      
    // Function that returns true 
    // if num is palindrome 
    static bool isPalindrome(int num) 
    { 
      
        // If the number is equal to the 
        // reverse of it then it 
        // is a palindrome 
        if (num == reverse(num)) 
            return true; 
      
        return false; 
    } 
      
    // Function to print all the 
    // d-digit palindrome numbers 
    static void printPalindromes(int d) 
    { 
        if (d <= 0) 
            return; 
      
        // Smallest and the largest d-digit numbers 
        int smallest = (int)Math.Pow(10, d - 1); 
        int largest = (int)Math.Pow(10, d) - 1; 
      
        // Starting from the smallest d-digit 
        // number till the largest 
        for (int i = smallest; i <= largest; i++)
        { 
  
            // If the current number 
            // is palindrome 
            if (isPalindrome(i)) 
                Console.Write(i + " "); 
        } 
    } 
      
    // Driver code 
    public static void Main (String[] args)
    { 
        int d = 2; 
      
        printPalindromes(d); 
    } 
}
  
// This code is contributed by Rajput-Ji

输出：

11 22 33 44 55 66 77 88 99