new questions added

Author: arorarahul

README.md

@@ -46,6 +46,8 @@ TODO:
 - radix sort for d digit numbers
 - find maximum sum subarray from an array
 - find triplet that sums to given value using binary search technique
+- make a circular linked list with a sentinel
+- double linked list insertion all points and deletion
 
 ### General Questions
 
@@ -110,6 +112,9 @@ TODO:
 - [Program to create a singly linked list, insert and delete nodes and print all of them](/linked-lists/question1.c)
 - [Move the last node to the begining of a linked list](/linked-lists/question2.c)
 - [Traverse a Single linked list using recursion](/linked-lists/question3.c)
+- [Iterative program to reverse a linked list](/linked-lists/question4.c)
+- [Recursive program to reverse a linked list](/linked-lists/question5.c)
+
 
 ## Some important concepts to solve algos better
 

linked-lists/question2.c

@@ -44,16 +44,18 @@ int main(){
 	t = head;
 	printList(t,head);
 	struct node *p;
+
 	while(t->link){
 		p = t;
-		t = t->link;
+		t=t->link;
 	}
-	t->link = NULL;
-	// free(t);
-	p->next = head;
-	head = p;
 
-	t = head;
+	free(t);
+
+	t->link = head;
+	p->link = NULL;
+	head = t;
+
 	printList(t,head);
 
 }

linked-lists/question4.c

@@ -0,0 +1,60 @@
+/*
+Iterative program to reverse a linked list
+*/
+#include <stdio.h>
+#include <stdlib.h>
+
+struct node{
+	int data;
+	struct node *link;
+};
+
+void printList(struct node *t){
+	if(t){
+		//interchanging these lines will print it in reverse order
+		printf("%d\n", t->data);
+		printList(t->link);
+	}
+}
+
+int main(){
+
+	struct node *head = (struct node *)malloc(sizeof(struct node));
+
+	struct node *t = head;
+
+	int counter = 1;
+	while(counter<=5){
+
+		t->data = counter*10;
+		if(counter == 5){
+			t->link = NULL;
+		}else{
+			t->link = (struct node *)malloc(sizeof(struct node));
+		}
+
+		t = t->link;
+
+		counter++;
+	}
+	t = head;
+	printList(t);
+	t = head;
+	
+	//reversing the list
+	struct node *curr, *prev,*nextNode;
+	curr = head;
+	
+	prev = NULL;
+	while(curr){
+		nextNode = curr->link;
+		curr->link = prev;
+		prev = curr;
+		curr = nextNode;
+		
+	}
+	head = prev;
+
+	printList(head);
+
+}	

linked-lists/question5.c

@@ -0,0 +1,44 @@
+/*
+Recursive program to reverse a linked list
+*/
+
+struct node{
+	int data;
+	struct node *link;
+};
+
+void printList(struct node *t){
+	if(t){
+		//interchanging these lines will print it in reverse order
+		printf("%d\n", t->data);
+		printList(t->link);
+	}
+}
+
+int main(){
+
+	struct node *head = (struct node *)malloc(sizeof(struct node));
+
+	struct node *t = head;
+
+	int counter = 1;
+	while(counter<=5){
+
+		t->data = counter*10;
+		if(counter == 5){
+			t->link = NULL;
+		}else{
+			t->link = (struct node *)malloc(sizeof(struct node));
+		}
+
+		t = t->link;
+
+		counter++;
+	}
+	t = head;
+	printList(t);
+	t = head;
+
+	
+
+}