Extra long factorials

Problem Statement

You are given an integer N. Print the factorial of this number.

N!=N×(N−1)×(N−2)×⋯×3×2×1

Note: Factorials of N>20 can't be stored even in a 64−bit long long variable. Big integers must be used for such calculations. Languages like Java, Python, Ruby etc. can handle big integers but we need to write additional code in C/C++ to handle such large values.

We recommend solving this challenge using BigIntegers.

Input Format Input consists of a single integer N.

Constraints 1≤N≤100

Output Format Output the factorial of N.

Sample Input 25

Sample Output 15511210043330985984000000

Reverse a doubly linked list

Problem Statement

You’re given the pointer to the head node of a doubly linked list. Reverse the order of the nodes in the list. The head node might be NULL to indicate that the list is empty.

Input Format You have to complete the Node* Reverse(Node* head) method which takes one argument - the head of the doubly linked list. You should NOT read any input from stdin/console.

Output Format Change the next and prev pointers of all the nodes so that the direction of the list is reversed. Then return the head node of the reversed list. Do NOT print anything to stdout/console.

Sample Input

NULL NULL <-- 2 <--> 4 <--> 6 --> NULL

Sample Output NULL NULL <-- 6 <--> 4 <--> 2 --> NULL

Explanation 1. Empty list, so nothing to do. 2. 2,4,6 become 6,4,2 o reversing in the given doubly linked list.

Print in Reverse

Problem Statement

You are given the pointer to the head node of a linked list and you need to print all its elements in reverse order from tail to head, one element per line. The head pointer may be null meaning that the list is empty - in that case, do not print anything!

Input Format You have to complete the void ReversePrint(Node* head) method which takes one argument - the head of the linked list. You should NOT read any input from stdin/console.

Output Format Print the elements of the linked list in reverse order to stdout/console (using printf or cout) , one per line.

Sample Input

1 --> 2 --> NULL 2 --> 1 --> 4 --> 5 --> NULL

Sample Output 2 1 5 4 1 2

Explanation 1. First list is printed from tail to head hence 2,1 2. Similarly second list is also printed from tail to head.