C Program to check if an Array is Palindrome or not

Given an array arr[] of any size n, our task is to find out whether the array is palindrome or not. A palindrome is a sequence which reads the same backwards and forwards, like: MADAM, NAMAN, etc.

To check if an array is palindrome, we compare elements from both ends moving towards the center −

Syntax

int isPalindrome(int arr[], int n);

Example 1: Palindrome Array

#include <stdio.h>

int isPalindrome(int arr[], int n) {
    int i, j;
    for(i = 0, j = n - 1; i < j; i++, j--) {
        if(arr[i] != arr[j]) {
            return 0; // Not palindrome
        }
    }
    return 1; // Palindrome
}

int main() {
    int arr[] = {1, 2, 3, 2, 1};
    int n = sizeof(arr) / sizeof(arr[0]);
    
    if(isPalindrome(arr, n)) {
        printf("Array is palindrome
");
    } else {
        printf("Array is not palindrome
");
    }
    
    return 0;
}

Array is palindrome

Example 2: Non-Palindrome Array

#include <stdio.h>

int isPalindrome(int arr[], int n) {
    for(int i = 0; i < n / 2; i++) {
        if(arr[i] != arr[n - 1 - i]) {
            return 0;
        }
    }
    return 1;
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    
    printf("Array: ");
    for(int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("
");
    
    if(isPalindrome(arr, n)) {
        printf("Array is palindrome
");
    } else {
        printf("Array is not palindrome
");
    }
    
    return 0;
}

Array: 1 2 3 4 5 
Array is not palindrome

How It Works

The algorithm compares elements from both ends of the array moving towards the center:

• Two-pointer approach: Use indices i and j starting from opposite ends
• Comparison: Check if arr[i] == arr[j] at each step
• Early termination: If any pair doesn't match, return false immediately
• Time complexity: O(n/2) which is O(n)
• Space complexity: O(1) − constant extra space

Key Points

• Only need to check up to the middle of the array (n/2 comparisons)
• Arrays with single element or empty arrays are considered palindromes
• The function returns 1 for palindrome and 0 for non-palindrome

Conclusion

Checking if an array is palindrome involves comparing elements from both ends moving towards the center. This two-pointer approach provides an efficient O(n) solution with constant space complexity.