From 8f5a91a28462e01507fb0eeeb8dc005b572e9efd Mon Sep 17 00:00:00 2001
From: ayush26sharma <58669560+ayush26sharma@users.noreply.github.com>
Date: Fri, 29 Oct 2021 11:08:08 +0530
Subject: [PATCH] Added some useful functions for singly linked list.

Added three functions in total for singly linked list:
1. reverseList- basically the reverse list from a given position in the list till the end.
a->b->c->d->e->f
reverseList(c)
 a->b->f->e->d->c

2. detectLoop - It detects the loop in a given singly linked list using Floyd's tortoise and hare algorithm.
a->b->c->d->e->f->g->h->c
linkedlist.detectLoop() gives true in this case.

3. swapNodes - It simply swaps the two given nodes themselves and not just their data. (In place swapping)
a->b->c->d->e->f
swapNodes(b,e)
a->e->c->d->b->f
---
 DataStructures/Lists/SinglyLinkedList.java | 59 +++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

diff --git a/DataStructures/Lists/SinglyLinkedList.java b/DataStructures/Lists/SinglyLinkedList.java
index 7e7b6166948f..2457bb3a6376 100644
--- a/DataStructures/Lists/SinglyLinkedList.java
+++ b/DataStructures/Lists/SinglyLinkedList.java
@@ -74,7 +74,64 @@ public void insertNth(int data, int position) {
     cur.next = newNode;
     size++;
   }
-
+  
+  /**
+  Detects if there is a loop in the singly linked list
+  using floy'd turtle and hare algorithm.
+  **/
+  public boolean detectLoop(){
+    Node currentNodeFast = head;
+    Node currentNodeSlow = head;
+    boolean flag = false;
+    while(currentNodeFast!=null && currentNodeFast.next != null && currentNodeSlow!=null && currentNodeSlow.next != null){
+        currentNodeFast = currentNodeFast.next.next;
+        currentNodeSlow = currentNodeSlow.next;
+        if (currentNodeFast==currentNodeSlow){
+            flag = true;
+            break;
+        }
+      }
+    return flag;
+    }
+  
+  /**
+  Swaps nodes of two given values a and b.
+  **/
+  
+  public void swapNodes(int a, int b){
+        Node currentNode = head;
+        Node temp = null;
+        while(currentNode!=null){
+            if (currentNode.next.value == a){
+                temp = currentNode.next;
+            }
+            if(currentNode.next.value == b){
+                currentNode.next=temp;
+            }
+            currentNode=currentNode.next;
+        }
+    }
+  
+  
+  /**
+  Reverse a singly linked list from a given node till the end
+  **/
+    
+    
+  Node reverseList(Node node) {
+      Node prev = null, curr = node, next;
+      while (curr != null) {
+          next = curr.next;
+          curr.next = prev;
+          prev = curr;
+          curr = next;
+      }
+      node = prev;
+      return node;
+  }
+  
+  
+  
   /** Deletes a node at the head */
   public void deleteHead() {
     deleteNth(0);