Table Of ContentELEMENTS OF
PROGRAMMING
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INTERVIEWS
Java A
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ADNAN AZIZ
TSUNG-HSIEN LEE
AMIT PRAKASH
Elements of
Programming
Interviews in Java
The Insiders' Guide
Adnan Aziz
Tsung-Hsien Lee
Amit Prakash
ElementsOfProgramminglnterviews.com
Adnan Aziz is a Research Scientist at Facebook. Previously, he was a professor at
the Department of Electrical and Computer Engineering at The University of Texas
at Austin, where he conducted research and taught classes in applied algorithms. He
received his Ph.D. from The University of California at Berkeley; his undergraduate
degree is from Indian Institutes of Technology Kanpur. He has worked at Google,
Qualcomm, IBM, and several software startups. When not designing algorithms, he
plays with his children, Laila, Imran, and Omar.
Tsung-Hsien Lee is a Senior Software Engineer at Uber. Previously, he worked
as a Software Engineer at Google and as Software Engineer Intern at Facebook.
He received both his M.S. and undergraduate degrees from National Tsing Hua
University. He has a passion for designing and implementing algorithms. He likes
to apply algorithms to every aspect of his life. He takes special pride in helping to
organize Google Code Jam 2014 and 2015.
Amit Prakash is a co-founder and CTO of ThoughtSpot, a Silicon Valley startup.
Previously, he was a Member of the Technical Staff at Google, where he worked
primarily on machine learning problems thatarise in thecontext of onlineadvertising.
Before that he worked at Microsoft in the web search team. He received his Ph.D.
from The University of Texas at Austin; his undergraduate degree is from Indian
Institutes of Technology Kanpur. When he is not improving business intelligence, he
indulges in his passion for puzzles, movies, travel, and adventures with Nidhi and
Aanya.
Elements of Programming Interviews: The Insiders' Guide
by Adnan Aziz, Tsung-Hsien Lee, and Amit Prakash
Copyright © 2015 Adnan Aziz, Tsung-Hsien Lee, and Amit Prakash. All rights
reserved.
No part of this publication may be reproduced, stored in a retrieval system, or trans¬
mitted, in any form, or by any means, electronic, mechanical, photocopying, record¬
ing, or otherwise, without the prior consent of the authors.
The views and opinions expressed in this work are those of the authors and do not
necessarily reflect the official policy or position of their employers.
We typeset this book using PTpX and the Memoir class. We used TikZ to draw figures.
Allan Ytac created the cover, based on a design brief we provided.
The companion website for the book includes contact information and a list of known
errors for each version of the book. If you come across an error or an improvement,
please let us know.
Version 2.0.0
Website: http://elementsofprogramminginterviews.com
To my father, Ishrat Aziz,
forgiving me my lifelong love of learning
Adnan Aziz
To my parents, Hsien-Kuo Lee and Tseng-Hsia Li,
for the everlasting support and love they give me
Tsung-Hsien Lee
To my parents, Manju Shree and Arun Prakash,
the most loving parents I can imagine
Amit Prakash
Table of Contents
Introduction 1
I The Interview 6
1 Getting Ready 7
2 Strategies For A Great Interview 13
3 Conducting An Interview 20
4 Problem Solving 24
II Problems 43
5 Primitive Types 44
5.1 Computing the parity of a word 45
5.2 Swap bits 48
5.3 Reverse bits 49
5.4 Find a closest integer with the same weight 50
5.5 Compute x X y without arithmetical operators 51
5.6 Compute x/y 52
5.7 Compute xv 53
5.8 Reverse digits 54
5.9 Check if a decimal integer is a palindrome 55
5.10 Generate uniform random numbers 56
5.11 Rectangle intersection 57
6 Arrays 60
6.1 The Dutch national flag problem 62
6.2 Increment an arbitrary-precision integer 65
I
6.3 Multiply two arbitrary-precision integers 66
6.4 Advancing through an array 68
6.5 Delete duplicates from a sorted array 69
6.6 Buy and sell a stock once 70
6.7 Buy and sell a stock twice 71
6.8 Enumerate all primes to n 72
6.9 Permute the elements of an array 74
6.10 Compute the next permutation 76
6.11 Sample offline data 78
6.12 Sample online data 79
6.13 Compute a random permutation 81
6.14 Compute a random subset 82
6.15 Generate nonuniform random numbers 83
6.16 The Sudoku checker problem 85
6.17 Compute the spiral ordering of a 2D array 87
6.18 Rotate a 2D array 90
6.19 Compute rows in Pascal's Triangle 92
7 Strings 94
7.1 Interconvert strings and integers 95
7.2 Base conversion 96
7.3 Compute the spreadsheet column encoding 98
7.4 Replace and remove 98
7.5 Test palindromicity 100
7.6 Reverse all the words in a sentence 101
7.7 Compute all mnemonics for a phone number 102
7.8 The look-and-say problem 104
7.9 Convert from Roman to decimal 105
7.10 Compute all valid IP addresses 106
7.11 Write a string sinusoidally 107
7.12 Implement run-length encoding 108
7.13 Find the first occurrence of a substring 109
8 Linked Lists 112
8.1 Merge two sorted lists 115
8.2 Reverse a single sublist 116
8.3 Test for cyclicity 117
8.4 Test for overlapping lists—lists are cycle-free 119
8.5 Test for overlapping lists—lists may have cycles 121
8.6 Delete a node from a singly linked list 122
8.7 Remove the kth last element from a list 123
8.8 Remove duplicates from a sorted list 124
8.9 Implement cyclic right shift for singly linked lists 125
8.10 Implement even-odd merge 126
8.11 Test whether a singly linked list is palindromic 127
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8.12 Implement list pivoting 128
8.13 Add list-based integers 129
9 Stacks and Queues 131
9.1 Implement a stack with max API 132
9.2 Evaluate RPN expressions 135
9.3 Test a string over for well-formedness 137
9.4 Normalize pathnames 138
9.5 Search a postings list 139
9.6 Compute buildings with a sunset view 140
9.7 Compute binary tree nodes in order of increasing depth 143
9.8 Implement a circular queue 145
9.9 Implement a queue using stacks 146
9.10 Implement a queue with max API 147
10 Binary Trees 150
10.1 Test if a binary tree is height-balanced 152
10.2 Test if a binary tree is symmetric 154
10.3 Compute the lowest common ancestor in a binary tree 155
10.4 Compute the LCA when nodes have parent pointers 157
10.5 Sum the root-to-leaf paths in a binary tree 158
10.6 Find a root to leaf path with specified sum 159
10.7 Implement an inorder traversal without recursion 160
10.8 Implement a preorder traversal without recursion 161
10.9 Compute the fcth node in an inorder traversal 162
10.10 Compute the successor 163
10.11 Implement an inorder traversal with 0(1) space 164
10.12 Reconstruct a binary tree from traversal data 165
10.13 Reconstruct a binary tree from a preorder traversal with markers . 167
10.14 Form a linked list from the leaves of a binary tree 168
10.15 Compute the exterior of a binary tree 169
10.16 Compute the right sibling tree 171
10.17 Implement locking in a binary tree 173
11 Heaps 175
11.1 Merge sorted files 177
11.2 Sort an increasing-decreasing array 179
11.3 Sort an almost-sorted array 180
11.4 Compute the k closest stars 181
11.5 Compute the median of online data 182
11.6 Compute the k largest elements in a max-heap 184
11.7 Implement a stack API using a heap 185
12 Searching 187
12.1 Search a sorted array for first occurrence of k 190
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12.2 Search a sorted array for entry equal to its index 191
12.3 Search a cyclically sorted array 192
12.4 Compute the integer square root 194
12.5 Compute the real square root 195
12.6 Search in a 2D sorted array 196
12.7 Find the min and max simultaneously 198
12.8 Find the fcth largest element 199
12.9 Find the missing IP address 202
12.10 Find the duplicate and missing elements 203
13 Hash Tables 207
13.1 Test for palindromic permutations 212
13.2 Is an anonymous letter constructible? 213
13.3 Implement an ISBN cache 214
13.4 Compute the LCA, optimizing for close ancestors 216
13.5 Compute the k most frequent queries 217
13.6 Find the nearest repeated entries in an array 217
13.7 Find the smallest subarray covering all values 218
13.8 Find smallest subarray sequentially covering all values 222
13.9 Find the longest subarray with distinct entries 224
13.10 Find the length of a longest contained interval 225
13.11 Compute the average of the top three scores 227
13.12 Compute all string decompositions 228
13.13 Test the Collatz conjecture 230
13.14 Implement a hash function for chess 231
14 Sorting 234
14.1 Compute the intersection of two sorted arrays 236
14.2 Merge two sorted arrays 238
14.3 Remove first-name duplicates 239
14.4 Render a calendar 240
14.5 Merging intervals 242
14.6 Compute the union of intervals 244
14.7 Partitioning and sorting an array with many repeated entries . . . 246
14.8 Team photo day—1 248
14.9 Implement a fast sorting algorithm for lists 250
14.10 Compute a salary threshold 252
15 Binary Search Trees 254
15.1 Test if a binary tree satisfies the BST property 256
15.2 Find the first key greater than a given value in a BST 259
15.3 Find the k largest elements in a BST 260
15.4 Compute the LCA in a BST 261
15.5 Reconstruct a BST from traversal data 262
15.6 Find the closest entries in three sorted arrays 265
IV
15.7 Enumerate numbers of the form a + bÿJl 267
15.8 The most visited pages problem 269
15.9 Build a minimum height BST from a sorted array 271
15.10 Insertion and deletion in a BST 272
15.11 Test if three BST nodes are totally ordered 275
15.12 The range lookup problem 276
15.13 Add credits 279
16 Recursion 282
16.1 The Towers of Hanoi problem 283
16.2 Generate all nonattacking placements of n-Queens 285
16.3 Generate permutations 287
16.4 Generate the power set 289
16.5 Generate all subsets of size k 291
16.6 Generate strings of matched parens 292
16.7 Generate palindromic decompositions 293
16.8 Generate binary trees 295
16.9 Implement a Sudoku solver 296
16.10 Compute a Gray code 298
16.11 Compute the diameter of a tree 300
17 Dynamic Programming 303
17.1 Count the number of score combinations 306
17.2 Compute the Levenshtein distance 309
17.3 Count the number of ways to traverse a 2D array 312
17.4 Compute the binomial coefficients 314
17.5 Search for a sequence in a 2D array 315
17.6 The knapsack problem 317
17.7 The bedbathandbeyond.com problem 320
17.8 Find the minimum weight path in a triangle 323
17.9 Pick up coins for maximum gain 324
17.10 Count the number of moves to climb stairs 326
17.11 The pretty printing problem 327
17.12 Find the longest nondecreasing subsequence 330
18 Greedy Algorithms and Invariants 333
18.1 Compute an optimum assignment of tasks 334
18.2 Schedule to minimize waiting time 335
18.3 The interval covering problem 336
18.4 The 3-sum problem 340
18.5 Find the majority element 341
18.6 The gasup problem 343
18.7 Compute the maximum water trapped by a pair of vertical lines . . 345
18.8 Compute the largest rectangle under the skyline 347
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