Finding the longest palindrome in an array in C++

October 11, 2022

Longest Palindrome in an array in C++

Here, in this page we will discuss the program to find the longest palindrome in an array in C++ programming language. We are given with an array and need to print the longest palindromic element in the given array.

Sorting element in array by frequency in C++
While loop in C

Here, we will discuss the following methods to print the longest palindromic number in the given input array.

  • Method 1 : Using Naive Approach
  • Method 2 : Using Sorting

 

Method 1 :

  • Create a function ispalindrome(int n), it will return 1 if the passing number is palindrome otherwise return 0.
  • Inside the main function, create a variable say res =INT_MIN, that hold the maximum palindrome number.
  • Run a loop from [0, n),  and check if(ispalindrome(arr[i]) && res<arr[i]), then set res = arr[i].
  • After complete iteration, check if(res==INT_MIN), set res = -1;
  • Print the value of res.
Longest palindrome in an array in C++

Finding the frequency of elements in an array

Sorting elements of an array by frequency

Counting Distinct Elements in an Array

Finding  Repeating elements in an Array

Finding Non Repeating elements in an Array

Method 1 : Code in C++

Run 
#include<bits/stdc++.h>
using namespace std;

int ispalindrome(int n){
    int rev=0, temp = n;

    while(temp>0){
       int rem = temp%10;
       rev = rev*10 + rem;
       temp /= 10;
    }

    if(n==rev)
       return 1;

    return 0;
}

int main(){
     int arr[] = {1, 121, 55551, 545545, 10111, 90};
     int n = sizeof(arr)/sizeof(arr[0]);
     int res = INT_MIN;

     for(int i=0; i<n; i++){
       if(ispalindrome(arr[i]) && res<arr[i])
          res = arr[i];
     }

     if(res==INT_MIN)
        res = -1;

     cout<<res;
}

Output

545545

Method 2 :

In this method we first sort the array and then start traversing the array from end, and return the element that satisfy the condition, that it is palindrome.

Method 2 : Code in C++

Run 
#include<bits/stdc++.h>
using namespace std;

int ispalindrome(int n){
    int rev=0, temp = n;

    while(temp>0){
        int rem = temp%10;
        rev = rev*10 + rem;
        temp /= 10;
    }

    if(n==rev)
       return 1;

    return 0;
}

int main(){
    int arr[] = {1, 121, 55551, 545545, 10111, 90};
    int n = sizeof(arr)/sizeof(arr[0]);
    int res = INT_MIN;

    sort(arr, arr+n);
    for(int i=n-1; i>=0; i--){
        if(ispalindrome(arr[i]) && res<arr[i]){
           res = arr[i];
           break;
        }
    }

    if(res==INT_MIN)
      res = -1;

    cout<<res;
}

Output

545545

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