71 lines
1.8 KiB
Java
71 lines
1.8 KiB
Java
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package DataStructures.Stacks;
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import java.util.Scanner;
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import java.util.Stack;
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/**
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* Reversal of a stack using recursion.
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*
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* @author Ishika Agarwal, 2021
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*/
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public class ReverseStack {
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public static void main(String args[]){
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Scanner sc = new Scanner(System.in);
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System.out.println("Enter the number of elements you wish to insert in the stack");
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int n = sc.nextInt();
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int i;
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Stack<Integer> stack = new Stack<Integer>();
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System.out.println("Enter the stack elements");
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for(i = 0; i < n ; i++)
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stack.push(sc.nextInt());
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sc.close();
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reverseStack(stack);
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System.out.println("The reversed stack is:");
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while(!stack.isEmpty()){
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System.out.print(stack.peek()+",");
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stack.pop();
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}
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}
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private static void reverseStack(Stack<Integer> stack) {
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if(stack.isEmpty()){
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return;
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}
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//Store the topmost element
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int element = stack.peek();
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//Remove the topmost element
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stack.pop();
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//Reverse the stack for the leftover elements
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reverseStack(stack);
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//Insert the topmost element to the bottom of the stack
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insertAtBottom(stack,element);
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}
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private static void insertAtBottom(Stack<Integer> stack, int element) {
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if(stack.isEmpty()){
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//When stack is empty, insert the element so it will be present at the bottom of the stack
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stack.push(element);
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return;
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}
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int ele = stack.peek();
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/*Keep popping elements till stack becomes empty. Push the elements once the topmost element has
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moved to the bottom of the stack.
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*/
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stack.pop();
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insertAtBottom(stack, element);
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stack.push(ele);
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}
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}
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