Cracking the Coding Interview - 7 steps - Udacity

Gayle L.McDowell | Founder / CEO

gayle in/gaylemcdgayle

Cracking theCoding Interview

CareerCup

gayle in/gaylemcdgayleGayle Laakmann McDowell 2

Hi! I’m Gayle Laakmann McDowell

Author Interview Coach Interview Consulting

<dev>

</dev>

(CS)

(MBA)

What We Look ForThings that make you think01

Gayle Laakmann McDowell 4gayle in/gaylemcdgayle

Why?

Analytical skills

How you think Make

tradeoffs

Push through hard problems

Communication Strong CS

fundamentals

gayle in/gaylemcdgayle 5

z

Gayle Laakmann McDowell

Whatis NOT

expected

To know the answers To solve immediately To code perfectly

(It’s nice. It just doesn’t

happen*.)

* Okay fine. It happened once, in 2000+ hiring packets.


z


WhatIS

expected

Be excited about hard problems

Drive! Keep trying when stuck More than just “correct”

Pay attention to me! Write real code

Show me how you think!

Preparation02


Essential KnowledgeData Structures

Algorithms Concepts

ArrayLists Merge Sort Big O Time

Hash Tables Quick Sort Big O Space

Trees (+ Tries) & Graphs

Breadth-First Search

Recursion

Linked Lists Depth-First Search

Memoization / Dynamic Programming

Stacks / Queues Binary Search

Heaps


Preparation

MASTER Big O Implement DS/Algorithms Practice with interview questions Code on paper/whiteboard Mock interviews

PUSH YOURSELF!

7 StepsThings that make you think03


z


HowTo

Approach

Crac

king

TheC

odin

gInt

ervi

ew.c

om

“R

esou

rces

”

gayle in/gaylemcdgayle 12Gayle Laakmann McDowell

step

1Listen (for clues)


step

2Draw an Example INTERSECTION SIZE:

Find # elements in common between two sorted, distinct arrays:


Ex: Intersection of Two Sorted Arrays

Most people draw something like this:

[1, 12, 15, 19][2, 12, 13, 20]

Too small Too special-case-y • same size, one common element, same

index


Ex: Intersection of Two Sorted Arrays

Better:[1, 12, 15, 19, 20, 21][2, 15, 17, 19, 21, 25,

27] Big No special cases


step

2Draw an Example

Big Enough

General Purpose

+


step

3Brute Force / Naive

Stupid & terrible is okay!


step

4Optimize

Walk through

brute force

Look for optimizations


Techniques to Develop Algorithms

BUD Space and Time Do It Yourself

Push yourself!


(A) Look for BUD

BottlenecksUnnecessary workDuplicated work


What’s the bottleneck?

Ex: counting the intersection[1, 12, 15, 19, 20, 21][2, 15, 17, 19, 21, 25, 27]

Brute Force: O(A * B) Bottleneck: O(B) to search

Binary Search Algorithm: O(A log B) Bottleneck: O(log B) to search

Sorted Merge: O(A + B) B


What’s unnecessary?

Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000

Unnecessary: looking for d U


What’s unnecessary?

Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000

Unnecessary: looking for d U


What’s duplicated?

Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000

Duplicated: c, d pairs D



Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000


c d c3 + d3

… … …4 31 298554 32 328324 33 36001… … …5 59 2055045 60 2161255 61 227106… … …



Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000


c3 + d3 (c, d)… …29855 (4, 31)32832 (4, 32), (18, 30)36001 (4, 33)… …205504 (5, 59)216125 (5, 60), (45, 50)227106 (5, 61)… …



Ex: a3 + b3 = c3 + d3 (1 <= a, b, c, d <= 1000

D


(B) Space/Time Tradeoffs

Hash tables & other data structures

Precomputing


(C) Do it yourself

Find permutations of s within b


find abbcd inbabc dbaef dbbac bddf ae0 1 2 3 4 5 6 7 8 9 10 1

1 12 13 14 15 16 17 18 19


(C) Do it yourself

Find permutations of s within b s = abbcd b =

Find them! … now how did you actually do it?

babc dbaef dbbac bddf ae


Techniques to Develop Algorithms

BUD Space and Time Do It Yourself Push yourself!


step

5Walk Through

Know the variablesand when they change


step

6Write Beautiful Code


How to Write Whiteboard Code

Top-left corner Short Hand

Helps

Good style Modularize

(upfront!)


Short Hand Helps

Good:

Good Enough & Easier:


Good Style

Appropriate & Consistent Spacing

Good Variable NamesBAD


Modularization


step

7Testing

FIRST Analyze What’s it doing? Why? Anything that looks

weird? Error hot spots

THEN use test cases Small test cases Edge cases Bigger test cases

BUT… Test code, not algorithm Think as you test Think before you fix


z


HowTo

Approach

Crac

king

TheC

odin

gInt

ervi

ew.c

om

“R

esou

rces

”

If you forget everything elsePlease remember this04


Please please please please

Create example Big (tiny is useless) Generic (not a special case)

Walk through it Figure out the output for that one input (Don’t worry about algorithms /

implementation) DO NOT CODE UNTIL YOU’RE

READY 100% sure that you know what you’re

doing 100% sure that your interview wants you

to code


Other Resources

Gayle.com

CareerCup.com

CrackingTheCodingInterview.com

Or, follow me online • facebook.com/gayle• twitter.com/gayle• gayle.com• [email protected]• quora.com