Write an algorithm to reverse a single linked list.

Question

Anonymous · Accepted Answer

class ListNode
{
public:
    int val;
    ListNode* next;
    ListNode(int x)
    {
        val=x; next=NULL;
    };
};
class Solution
{
    public :
    ListNode* ReverseList(ListNode* A)
    {
        stack  s;
        ListNode* temp=A,*ans;
        while (temp!=NULL)
        {
            s.push(temp);
            temp=temp->next;
        }
        temp=s.top();
        s.pop();
        ans=temp;
        while(!s.empty())
        {
            temp->next=s.top();
            temp=s.top();
            s.pop();
        }
        temp->next=NULL;
        return ans;
    }
};

Christine · Answer

using System;
using System.Collections.Generic;

public class Test
{
    public static void Main()
    {
        var linkedList = new LinkedList();
        linkedList.AddLast(1);
        linkedList.AddLast(3);
        linkedList.AddLast(5);
        
        var stack = new Stack();
        
        var reversedLinkedList = new LinkedList();
        
        
        Console.WriteLine("Linked List: ");
        var currNode = linkedList.First;
        while(currNode != null){
            stack.Push(currNode.Value);            
            Console.WriteLine(currNode.Value);            
            currNode = currNode.Next;
        }
        
        while (stack.Count > 0)
            reversedLinkedList.AddLast(stack.Pop());
        
       
        Console.WriteLine("Reversed List: ");
        currNode = reversedLinkedList.First;
        while(currNode != null){       
            Console.WriteLine(currNode.Value);            
            currNode = currNode.Next;
        }
    }
}

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