Seattle Tech
Interview
Topics

Big OH Notation
 Basics – to cover simple interviews.

Arrays
 Question

List
 Question

Stacks
 Question

Queues
 Question
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?
BIG O
What is the BIG O?
for (int i=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
What is the Big O
for (int i=0;i<n;i++ ){
for (int i=0;i<n;i++ ){
for (int j=0;j<n;j++){
print “hello”;
}
print “Hello”
}
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.
.Net stack 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 your array was 1000 – a[99] – still 1 operation
REMOVE( index of I)


If you know the index a[0]
A[i] = 0
REMOVE( VALUE )

Search for that N comparisons o(N)
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
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;
}
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);
}
Get the nth element ?
public Node get(int n){
Node n;
for (int i=0;i<n;i++){
if (node == null){
return null;
}
node = node.next;
}
return node;
}
Linked List

Add to a linked list
1. Get the location to insert.
2. Insert.
public void add(int n,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).
Linked List

FIND

INDEX OF

SIZE
Variations Of LinkedList

Single


HEADNEXTNEXT
Double
HEAD  NEXT  NEXT
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?
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
 23*
Stack

POP

PEEK

PUSH

EMPTY
Queue

ENQUEUE

DEQUEUE

PEEK
Stack In Action

Are the opening and closing brackets in
the right order.
Question

Implement a circular queue using arrays of a
given size?


enqueue()
dequeue()
Queues

BFS Tree Traversal.
Question