Stack Reversal

Problem Statement:
         In-place stack reversal using recursion.

Fig: In-place Stack Reversal

Source Code
Solution:
   Using recursion start from the bottom most element in the stack using the 1st Function Call(reverse()) , push each element to the bottom of the stack through recursion using another function call(pushToBottom()).

Below is the implementation.

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/** * Inplace reversal of Stack * @author Prateek */ public class ReverseStackRecursion { /** * Subroutine to Reverse the element of stack * @param stack : input stack */ public void reverseStack(Stack<Integer> stack){ if(stack.isEmpty()) return ; int val= stack.pop(); reverseStack(stack); pushToBottom(stack,val); return ; } /** * Pushes the incoming element or item to the bottom of the stack */ private void pushToBottom(Stack<Integer> stack,int item){ if(stack.isEmpty()){ stack.push(item); return ; } int val= stack.pop(); pushToBottom(stack,item); stack.push(val); } }

Happy Coding !! :)