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Data Structures/LinkedList/SinglyLinkedList/README.md

@@ -1,6 +1,7 @@
-# Singly Linked List 
 
+# Singly Linked List
 ## Complexity
+#### Time:
 - Time:
     - Access: 
         - Worst Case: ![formula](https://render.githubusercontent.com/render/math?math=O(n))
@@ -15,4 +16,32 @@
         - Worst Case: ![formula](https://render.githubusercontent.com/render/math?math=O(1))
         - Average Case: ![formula](https://render.githubusercontent.com/render/math?math=O(1))
 - Space:
-    - Worst Case: ![formula](https://render.githubusercontent.com/render/math?math=O(n))
+    - Worst Case: ![formula](https://render.githubusercontent.com/render/math?math=O(n))
+
+
+# Reverse a linked list
+
+
+## Demo
+Input: Head of following linked list 
+1->2->3->4->NULL 
+Output: Linked list should be changed to, 
+4->3->2->1->NULL
+
+Input: Head of following linked list 
+1->2->3->4->5->NULL 
+Output: Linked list should be changed to, 
+5->4->3->2->1->NULL
+
+## Algorithms
+Initialize three pointers prev as NULL, curr as head and next as NULL.
+Iterate through the linked list. In loop, do following. 
+// Before changing next of current, 
+// store next node 
+next = curr->next
+// Now change next of current 
+// This is where actual reversing happens 
+curr->next = prev 
+// Move prev and curr one step forward 
+prev = curr 
+curr = next

Data Structures/LinkedList/SinglyLinkedList/ReverseSinglyLinkList.cpp

@@ -0,0 +1,217 @@
+#include<iostream>
+
+using namespace std;
+
+
+struct node{
+int data;
+struct node * link;
+};
+
+struct node * start;
+
+void insertBegin(int item)
+{
+node * t= new node;
+t->data= item;
+
+// allocate memory for 1 node variable and t will be pointer to that node
+if( start== NULL)
+{
+start= t; t->link= NULL;
+}
+else
+{
+t->link= start;
+start= t;
+}
+cout<<" inserted at begin "<<item<<endl;
+
+}
+
+void insertLast(int item)
+{
+node * t= new node;
+t->data= item; t->link= NULL;
+if(start== NULL)
+{
+start= t ;
+}
+else{
+
+node * p= start;
+while(p->link!= NULL)
+{
+p= p->link;
+}
+p->link= t ; //p stores adress of current last node
+
+}
+cout<<"inserted at last "<<item<<endl;
+}
+void traverse()
+{
+node* p= start;
+while(p!= NULL)
+{
+cout<<p->data<<"-> ";
+p= p->link;
+}
+cout<<"NULL"<<endl;
+}
+
+void searchItem(int item)
+{
+node * p= start;
+while(p!= NULL)
+{
+if(item==p->data)
+{
+cout<<" found "<<item<<endl; return;
+}
+else
+{
+p= p->link;
+}
+}
+cout<<" not found "<<endl;
+}
+
+void insertAfter(int val, int item)
+{
+node * t= new node;
+t->data= item;
+if( start== NULL)
+{
+start= t; t->link= NULL;
+}
+else
+{
+node * p= start;
+while(p!= NULL)
+{
+if(val==p->data)
+{
+t->link= p->link;
+p->link= t;
+return;
+}
+else
+{
+p=p->link;
+}
+}
+
+}
+
+}
+
+void deleteBegin()
+{
+if(start== NULL)
+{
+cout<<"List is empty "<<endl; return;
+}
+else if(start->link==NULL)
+{
+node *p= start;
+start= NULL;
+delete p;
+}
+else
+{
+node *p= start;
+start= start->link;
+delete p;
+}
+}
+void deleteLast()
+{
+if(start==NULL)
+{
+cout<<"List is empty "<<endl; return;
+}
+else if(start->link==NULL)
+{
+node *p= start;
+start= NULL;
+delete p;
+}
+else
+{
+node *p,*t;
+p= start;
+while(p->link!= NULL)
+{
+t=p;
+p=p->link;
+}
+t->link= NULL;
+delete p;
+}
+}
+
+node * getMaxNode(){
+node *t,*p;
+
+if(start==NULL){ return NULL;}
+else
+{
+p= start;
+int mx= p->data; t= p;
+while(p!= NULL)
+{
+if(mx<p->data )
+{
+mx= p->data;
+t= p;
+}
+
+p= p->link;
+}
+
+}
+return t;
+}
+
+void reverseList()
+{
+    node * pre;
+    node * curr;
+    node * next;
+    pre =   NULL;
+    curr= start;
+    next = NULL;
+    while (curr!=NULL)
+
+    {
+         next= curr->link;
+         curr->link= pre;
+         pre = curr;
+         curr= next;
+
+    } start= pre;
+
+   return;    
+}
+int main()
+{
+insertLast(11);
+insertBegin(20);
+insertBegin(25);
+insertBegin(30);
+
+traverse();
+/*searchItem(25);
+searchItem(40);
+insertLast(22);
+traverse();
+insertAfter(20,70);
+traverse();
+deleteBegin();
+traverse();
+deleteLast();
+traverse();*/
+reverseList();
+traverse();
+}