Palindrome Program in C

Palindrome in c refers to the object that remains the same; even if we reverse the object, it remains the same as its original form. For example, "naman" is a palindrome as it remains the same when we reverse the string naman.

Algorithm

Logic to identify whether the given object is a palindrome or not is given below:

Algorithm 1

1. Obtain the input object, which is to be checked whether it is palindrome or not.
2. Now calculate the reverse of the input object and store it in another variable.
3. Now check whether the original input object obtained is equal to the reverse calculated and store the result to the bool variable.
4. If the calculated bool value is true, the given object is a palindrome; otherwise, the given object is not a palindrome.

• Time Complexity: $O(n)$ Here, we must traverse the whole string once; the time complexity is O(n).

• Space Complexity: $O(n)$ Here we need an extra space of the same array size as we need to reverse the string and store it; therefore, the space complexity is O(n).

Algorithm 2

1. Obtain the input object, which is to be checked whether it is palindrome or not.
2. Now, take two pointers, start pointer and end pointer. The start pointer points to the start of the input, and the end pointer points to the end.
3. Now check the values corresponding to both the pointers. Increment the start pointer and decrement the end pointer if the value at both pointers is the same; otherwise, break as the input is not a palindrome.
4. Repeat step 3 till either the start and end pointer point to the exact location or till the start pointer points to location (n/2), where n is the length of the input.

• Time Complexity: $O(n)$ We must traverse the whole string once, so the time complexity is O(n).

• Space Complexity: $O(1)$ We need extra space; therefore, the space complexity is O(1).

Palindrome Number Program in C

Algorithm 1

Here we would use a while loop to iterate over the string and reverse it. After reversing the string, we would compare both the strings and check whether it is a palindrome or not. For reversing, we would be traversing the whole string and storing its reverse in a new string rev using a while loop and after reversing, we would be comparing the string with the original string using strcmp() function, which returns 0 if both strings are identical and therefore if the string is same as reversed one, then it would return 0 which means that the given string is a Palindrome in c.

Code for Algorithm 1:

Output:

Output Explanation This Palindrome program in c successfully reverses the input string 'cabbac' and compares it with the original. Since both are identical, the program concludes that 'cabbac' is a palindrome.

Complexity Analysis

• Time Complexity: $O(N)$, where 'N' is the length of the string, accounting for the time taken to reverse and compare the string.
• Space Complexity: $O(N)$, due to the additional space required for storing the reversed string.

Algorithm 2

Here, we would be comparing start and end pointers and comparing characters one by one using a while loop, and in case any of the pointers do not match, then the given string would not be a Palindrome in c.

Code for Algorithm 2:

Output:

Output Explanation The Palindrome program in C checks each character from the start and end of the string. If all corresponding characters match, it confirms the string as a Palindrome in C. Otherwise, it's not a Palindrome number in C. This efficient approach avoids extra space, making it ideal for palindrome verification.

Complexity Analysis:

• Time Complexity: $O(N)$, where 'N' is the length of the string, as each character is checked at most once.
• Space Complexity: $O(1)$, indicating constant space usage regardless of input size, highlighting the efficiency of this C program to check palindrome.