Example: Longest Palindrome in Array (Iterative Digit Reversal) in C

// Longest Palindrome in Array (Iterative Digit Reversal)
#include <stdio.h>
#include <limits.h> // For INT_MIN

// Function to check if a number is a palindrome
// Returns 1 if palindrome, 0 otherwise
int isPalindrome(int num) {
    // Negative numbers are not typically considered palindromes
    // Single digit numbers (0-9) are palindromes
    if (num < 0) {
        return 0;
    }
    if (num >= 0 && num <= 9) {
        return 1;
    }

    int originalNum = num;
    int reversedNum = 0;

    // Step 1: Reverse the number
    while (num > 0) {
        int digit = num % 10;
        reversedNum = reversedNum * 10 + digit;
        num /= 10;
    }

    // Step 2: Compare the original number with the reversed number
    return originalNum == reversedNum;
}

// Function to count the number of digits in an integer
int countDigits(int num) {
    if (num == 0) {
        return 1;
    }
    int count = 0;
    // Handle negative numbers by converting to positive for digit counting
    if (num < 0) {
        num = -num;
    }
    while (num > 0) {
        num /= 10;
        count++;
    }
    return count;
}

int main() {
    int numbers[] = {121, 23, 4554, 9, 78987, 1001, 5, 987654321, 0, -121};
    int n = sizeof(numbers) / sizeof(numbers[0]);

    int longestPalindrome = INT_MIN; // Initialize with a value indicating no palindrome found
    int maxDigits = -1;
    int foundPalindrome = 0;

    printf("Array elements: ");
    for (int i = 0; i < n; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n\n");

    // Step 1: Iterate through each number in the array
    for (int i = 0; i < n; i++) {
        int currentNum = numbers[i];

        // Step 2: Check if the current number is a palindrome
        if (isPalindrome(currentNum)) {
            foundPalindrome = 1;
            int currentDigits = countDigits(currentNum);

            // Step 3: If it's a palindrome, compare its digit count with the maximum found so far
            if (currentDigits > maxDigits) {
                maxDigits = currentDigits;
                longestPalindrome = currentNum;
            }
        }
    }

    // Step 4: Print the result
    if (foundPalindrome) {
        printf("The longest palindrome in the array is: %d\n", longestPalindrome);
        printf("It has %d digits.\n", maxDigits);
    } else {
        printf("No palindromes found in the array.\n");
    }

    return 0;
}