Last Updated: 20 Feb, 2021

Insert An Element At Its Bottom In A Given Stack

Easy

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Problem statement

You are given a stack/deque of integers 'MY-STACK' and an integer ‘X’. Your task is to insert ‘X’ to the bottom of ‘MY-STACK’ and return the updated stack/deque.

Note :

If ‘MY_STACK’ = [7, 1, 4, 5], then the first element represents the element at the bottom of the stack and the last element represents the element at the top of the stack.

For Example :

Let ‘MY_STACK’ = [7, 1, 4, 5] and ‘X’ = 9. So, ‘MY_STACK’ after insertion becomes [9, 7, 1, 4, 5].

Example

Follow Up :

Try to do this without using any other data structure.

Input Format :

The first line of input contains a single integer T’, representing the number of test cases.

The first line of each test case contains two single space-separated numbers, ‘N’ and ‘X’, denoting the size of ‘MY_STACK’ and the integer to be inserted at the bottom, respectively.

The second line contains ‘N’ space-separated distinct integers denoting the stack/deque elements.

Output Format :

For each test case, print the elements of the updated ‘MY_STACK’ separated by a single space.

The output of every test case will be printed in a separate line.

Note :

You don’t have to print anything, it has already been taken care of. Just implement the given function.

Constraints :

1 <= T <=100
1 <= N <= 10^4
0 <= 'X’ and 'MY_STACK[i]’ <= 10^5

Time limit: 1 second

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Approaches

01 Approach

The idea is to use the recursion stack to achieve this task. So the base case will be when 'MY_STACK' is empty, that is when we will push the desired element. We will keep on extracting the top element of ‘MY_STACK’ recursively, delete it, make recursive calls and push the extracted element back into 'MY_STACK'.

Algorithm

Let’s say we have given a function ‘pushAtBottom’ that receives 2 parameters 'MY_STACK' and the element ‘X’ we need to push at the bottom. The working of this function is explained below:
- Base Case :
  - If 'MY_STACK' is empty, we push ‘X’ into 'MY_STACK'.
- Recursive calls:
  - We initialize and an integer variable says ‘NUM’ with the top element of 'MY_STACK'.
  - We pop from 'MY_STACK'.
  - We make a recursive call.
  - We push ‘NUM’ into 'MY_STACK'.
Finally, we return 'MY_STACK'.

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