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Data Structures : Lists

Abhilash I

abhilashi@students.iiit.ac.in

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Basics

In Cstruct node{

int data;struct node * next;

}

In C++struct node{

int data;node * next;

}

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Operations

Allocation of Memorystruct node *nn = (struct node *)malloc(sizeof(struct node)); //c

node *nn = new node; //c++ style

Insertion

Deletion

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Variants

Structural Variants

1. Single Linked List

2. Doubly Linked List

3. Circular LInked List

4. Circular Doubly Linked List

Ref:en.wikipedia.org/wiki/Linked

_list

http://en.wikipedia.org/wiki/Linked_listhttp://en.wikipedia.org/wiki/Linked_listhttp://en.wikipedia.org/wiki/Linked_listhttp://en.wikipedia.org/wiki/Linked_listhttp://en.wikipedia.org/wiki/Linked_listhttp://en.wikipedia.org/wiki/Linked_list

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Variants : operational

Stack LIFO

Queue FIFO

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Problems / questions (in interviews too)

To most of the questions naive solutions are trivial Yes, optimized versions are needed

We will walk through a set of problems in next slides

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Problem #1 Find the maximum/mininum elements of linked list ?

Trivial isn't it. A way to write the solution.

node* findMaximum(node *head){node * returnValue=head;while(head!=NULL){

if (head->data > returnValue->data){returnValue=head;

}head=head->next;

}return reuturnValue;}

Variable Naming/ Style of code is important

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Problem #2

Find Union/Intersection of two linked lists ? Typically you would have to write a function that returns a

new list, with specified criteria Write it down

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Problem #3

Reverse a given linked list Hottest problem that is always asked

1. Iterative solution2. Recursive solution

Constraints (da routine ones :P )1. O(1) Space2. O(n) Time

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Iterative Solution

void reverse(struct node **x){struct node *q,*r,*temp;r=*x;q=NULL;

while(r!=NULL){temp=q;q=r;r=r->next;q->next=temp;

}*x=p;

}

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Recursive Solution

node* reverse(node** head , node* cur){if(cur->next == NULL) {

*head = cur;}

else{(reverse(head,cur->next))->next = cur;cur->next = NULL;

}return cur;

}

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Trick: Moving Two pointers cleverly

Depends on the problem at hand. Example: Moving one pointer as

slow as Tortoise, and moving

another as fast as Hare. Also known as Floyd's cycledetection algorithm

Next 4 problems can be solvedusing this trick

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Problem #4

Find the kth element from the endof linked list ? Constraints

1. O(1) space2. O(n) time

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Problem #5 : The "Y" shaped Linked List

Given pointers to two singly-linked lists, find out if they arejoined and also at which node they are joined.

ConstriaintsO(1) space

O(N) time

Ref:Go to the link

http://blogs.msdn.com/abhinaba/archive/2007/08/16/interesting-linked-list-problem.aspx

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Problem #6

Find the centerof Linked List ? Constraint :

Without using integervariables

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Problem #7

Find whether a linked list has a cycle or not ? Possible approches

1. By storing the addresses all the elements already seen ?2. By destructing the linked list ?

What if we don't have auxilary storage and also do it withoutdestructing the list ?

Hint: Apply the intuition from previous slide Extension: Find the node at which the loop starts ?

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Problem #8:Not so easy deletion

Given a pointer to a node in a singly linked list delete thatparticular node.

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Problems for practice

1. Add two 100 digit numbers stored in a linked list

2. Check whether linked list is a palindrome. Each node storesa character

3. Swap two nodes of circular doubly linked list4. Sort linked list using quick, merge, insertion, selection sorts

5. Deleting Alternate nodes in the linked list6. XOR Linked List

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Stacks

Implement a stack using 2 queues efficiently Reverse a stack inplace Implement 3 stacks in an array You are given a black box datastructure which does

insertion and extract min in O(1) time. give an efficientimplementation for extract max using the operationssupported by it. What is the black box ? How to achieve this?

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cont

We are given with two arrays A and B..each of size N...elements of array contains either 1 or 0...

we have to find such an interval (p,q)(inclusive) such that

the sum of all the elements of A (between this interval) andsum of all elements of B (between this interval ) is equal...

i.e.

a[p]+a[p+1]....+a[q]= b[p]+b[p+1]....+b[q]

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Hope this presentation is of help :-)