Seattle Tech Interview

1. Seattle Tech Interview

2. Topics • Big OH Notation • Basics – to cover simple interviews. • Arrays • Question • List • Question • Stacks • Question • Queues • Question

3. BIG OH • Goal simplify Analysis of Algorithms by removing un wanted information • The basic goal is to understand • The limitations of a program • TIME • MEMORY • TIME • How much time does my program take as the input size increases? • Memory • How much memory will my program take as input size increases?

4. BIG O What is the BIG O? for (inti=0;i<n;i++ ){ for (int j=0;j<n;j++){ print “hello”; } print “Hello” } • How many Hellos will we print • (N^2) + 1 • When N =1 the last hello matters as it is 50% of the answer. • When N =1000 the last hello does not matter as it is .00001% of the answer. • Big OH implies what matters for large numbers - N^2

5. What is the Big O for (inti=0;i<n;i++ ){ for (inti=0;i<n;i++ ){ for (int j=0;j<n;j++){ print “hello”; } print “Hello” }

6. Arrays • Contiguous location of memory. • [1,2,3,4,5,6] • In Java • int [] a = new int[20]; always allocated on heap. • In C#,C++,Java values types are allocated in stack. • Typical JVM stack memory is 64KB. • .Netstack size 1M • Great when you know the number of elements you want to store. • You can pre allocate the memory and fill the spots. • ADD • If you know the index a[0] • If your array was 1000 – a[99] – still 1 operation • REMOVE( index of I) • A[i] = 0 • REMOVE( VALUE ) • Search for that N comparisons o(N)

7. Question on Array Find 2 numbers in an array that add up to a given number? Microsoft : Arrange the numbers in an array in alternating order. For example if the array is [a1, a2, a3, a4.. ]arrange the array such that b1<=b2>=b3<=b4 and so on. Sampe Input: 3 5 7 8 4 9 Sample Output: 3 < 5 > 4 < 8 >7 < 9

8. Linked List • How do we deal with situation when we don’t know the length of the elements we want to store. • Arrays[] – we need to know the length because the system allocates contiguous. • New Data structure Node{ int value; Node node; }

9. Linked List • Linked list • How do we move in the linked list? public void print(){ Node current = head; while (node.next != null){ System.out.println(node.value); }

10. Get the nth element ? public Node get(int n){ Node n; for (inti=0;i<n;i++){ if (node == null){ return null; } node = node.next; } return node; }

11. Linked List • Add to a linked list 1. Get the location to insert. 2. Insert. public void add(intn,int location){ PLEASE IMPLEMENT THE CODE. } Lets compare : • ADD • Since we don’t know the index – we have to traverse and then add to the end. O(N). • IF we decided to add to the head O(1). • REMOVE( index of I) • Travel to the index (i) and the remove O(N). • Compared to Array – O(1) • REMOVE( VALUE ) • Search for that N comparisons O(N). • Compared to Array O(N).

12. Linked List FIND INDEX OF SIZE

13. Variations Of LinkedList • Single • HEADNEXTNEXT • Double HEAD  NEXT  NEXT

14. Questions Reverse a linked list ( very common interview question) Given an integer linked list of which both first half and second half are sorted independently. Write a function to merge the two parts to create one single sorted linked list in place [do not use any extra]space]. How will you find a loop in a linked list. e.g. if the 4th node of the list is pointing back to the 2nd node (for a list of size 6), then it will be in a loop; how will you find this node?

15. Stacks & Queues • Using Arrays and Linked List • People decided to come up with Stacks and Queues. • Limited functionality • Only access to first element • Stack – first element is LAST entered. • Queue  First element is FIRST entered. • Typical usage • Processing postfix expression evaluation • 2 3 *

16. Stack POP PEEK PUSH EMPTY

17. Queue ENQUEUE DEQUEUE PEEK

18. Stack In Action • Are the opening and closing brackets in the right order.

19. Question • Implement a circular queue using arrays of a given size? • enqueue() • dequeue()

20. Queues BFS Tree Traversal.

21. Question