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Google Interview Questions
1. Why are manhole covers round?
Cause this is the shape that ensures they do not fall into hole.
2. What is the difference between a mutex and a semaphore? Which one would you use to protect access to an increment
operation?
Mutex is used to ensure that only one thread has access to resource. Semaphore has counter and allows up to defined
number threads access resource at the same time.
3. A man pushed his car to a hotel and lost his fortune. What happened?
Que?
4. Explain the significance of “dead beef”.
Term refers to hex number 0xdeadbeef = 3735928559. It is commonly used to detect buffer overflow and not initalized
variables.
5. Write a C program which measures the the speed of a context switch on a UNIX/Linux system.
Que?
6. Given a function which produces a random integer in the range 1 to 5, write a function which produces a random
integer in the range 1 to 7.
Randomizer.java – working code
Given: int get_1_to_5_int();
Solution:
int get_1_to_7_int() {
int result;
do {
result = get_1_to_5_int() + get_1_to_5_int() - 1;
} while (result > 7);
return result;
}
7. Describe the algorithm for a depth-first graph traversal.
MatrixGraph.java
In short DFS processes node after processing all its neighbors. Requires list of visited nodes. DFS should be started
for every not visited node.
8. Design a class library for writing card games.
TODO
9. You need to check that your friend, Bob, has your correct phone number, but you cannot ask him directly. You must
write a the question on a card which and give it to Eve who will take the card to Bob and return the answer to you.
What must you write on the card, besides the question, to ensure Bob can encode the message so that Eve cannot read
your phone number?
You need to use information you share with Bob and you have to be sure that Eve does not know it. E.g. Bob's number.
You can ask Bob to add digits of your number to his number mod 10. Knowing Bob's number you will be able to check if
Bob has your real number and Eve, who we assumed does not know Bob's number, won't be able to determine your number.
10. How are cookies passed in the HTTP protocol?
They are attached to http header. Set-cookie.
11. Design the SQL database tables for a car rental database.
CREATE TABLE CAR (
PLATE VARCHAR(7) PRIMARY KEY )
CREATE TABLE CUSTOMER (
ID INT PRIMARY KEY,
NAME VARCHAR(255),
SURNAME VARCHAR(255) )
CRETE TABLE RENTAL (
ID INT PRIMARY KEY,
CAR_PLATE VARCHR(7) FOREIGN KEY REFERENCES CAR(PLATE),
CUSTOMER_ID FOREIGN KEY REFERENCES CUSTOMER(ID),
DATE_FROM DATETIME,
DATE_TO DATETIME )
12. Write a regular expression which matches a email address.
^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$
13. Write a function f(a, b) which takes two character string arguments and returns a string containing only the
characters found in both strings in the order of a. Write a version which is order N-squared and one which is order N.
14. You are given a the source to a application which is crashing when run. After running it 10 times in a debugger,
you find it never crashes in the same place. The application is single threaded, and uses only the C standard library.
What programming errors could be causing this crash? How would you test each one?
Dependency on time, dependency on memory, dirty memory allocation, user input, null terminated strings.
Run static and dynamic code analysis.
15. Explain how congestion control works in the TCP protocol.
Never heard of it.
16. In Java, what is the difference between final, finally, and finalize?
Final means that value of variable cannot be changed after initialization.
Finally is one of try-catch-finally block. It ensures that bloc of code will be executed if control enters try block.
Finalize() is method of java.lang.Object. It is called by GC. Release of non-Java resources can be coded into
overridden finalize() method. It is also a good practice to call super.finalize() after releasing object's resources.
17. What is multithreaded programming? What is a deadlock?
Writing programs in a way that some tasks are executed in separate threads. It may then executed on different
cores / processors.
Deadlock is the situation when two or more threads request access to a resources to which they have access.
Thread T1 requests access to R1 and thread T2 requests access to R2, but in the same time Thread T1 has resource R2 and
thread T2 has resource R1.
18. Write a function (with helper functions if needed) called to Excel that takes an excel column value
(A,B,C,D…AA,AB,AC,… AAA..) and returns a corresponding integer value (A=1,B=2,… AA=26..).
private int calculateExcelColumnNumber(String columnName) {
int result = 0;
columnName.length();
int power = 1;
for(int i = columnName.length() - 1; i >= 0; i--) {
result += (columnName.charAt(i) - 'A' + 1) * power;
power *= 26;
}
return result;
}
19. You have a stream of infinite queries (ie: real time Google search queries that people are entering). Describe
how you would go about finding a good estimate of 1000 samples from this never ending set of data and then write code
for it.
20. Tree search algorithms. Write BFS and DFS code, explain run time and space requirements. Modify the code to handle
trees with weighted edges and loops with BFS and DFS, make the code print out path to goal state.
21. You are given a list of numbers. When you reach the end of the list you will come back to the beginning of the list
(a circular list). Write the most efficient algorithm to find the minimum # in this list. Find any given # in the list.
The numbers in the list are always increasing but you don’t know where the circular list begins,
ie: 38, 40, 55, 89, 6, 13, 20, 23, 36.
22. Describe the data structure that is used to manage memory. (stack)
23. What’s the difference between local and global variables?
24. If you have 1 million integers, how would you sort them efficiently? (modify a specific sorting algorithm to solve
this)
25. In Java, what is the difference between static, final, and const. (if you don’t know Java they will ask something
similar for C or C++).
26. Talk about your class projects or work projects (pick something easy)… then describe how you could make them more
efficient (in terms of algorithms).
27. Suppose you have an NxN matrix of positive and negative integers. Write some code that finds the sub-matrix with
the maximum sum of its elements.
28. Write some code to reverse a string.
29. Implement division (without using the divide operator, obviously).
30. Write some code to find all permutations of the letters in a particular string.
31. What method would you use to look up a word in a dictionary?
32. Imagine you have a closet full of shirts. It’s very hard to find a shirt. So what can you do to organize your
shirts for easy retrieval?
33. You have eight balls all of the same size. 7 of them weigh the same, and one of them weighs slightly more. How can
you fine the ball that is heavier by using a balance and only two weighings?
34. What is the C-language command for opening a connection with a foreign host over the internet?
35. Design and describe a system/application that will most efficiently produce a report of the top 1 million Google
search requests. These are the particulars:
1) You are given 12 servers to work with. They are all dual-processor machines with 4Gb of RAM, 4x400GB hard drives
and networked together.(Basically, nothing more than high-end PC’s)
2) The log data has already been cleaned for you. It consists of 100 Billion log lines, broken down into 12 320 GB
files of 40-byte search terms per line. 3) You can use only custom written applications or available free open-source
software.
36. There is an array A[N] of N numbers. You have to compose an array Output[N] such that Output[i] will be equal to
multiplication of all the elements of A[N] except A[i]. For example Output[0] will be multiplication of A[1] to A[N-1]
and Output[1] will be multiplication of A[0] and from A[2] to A[N-1]. Solve it without division operator and in O(n).
37. There is a linked list of numbers of length N. N is very large and you don’t know N. You have to write a function
that will return k random numbers from the list. Numbers should be completely random. Hint: 1. Use random function
rand() (returns a number between 0 and 1) and irand() (return either 0 or 1) 2. It should be done in O(n).
38, Find or determine non existence of a number in a sorted list of N numbers where the numbers range over M, M>> N
and N large enough to span multiple disks. Algorithm to beat O(log n) bonus points for constant time algorithm.
39. You are given a game of Tic Tac Toe. You have to write a function in which you pass the whole game and name of a
player. The function will return whether the player has won the game or not. First you to decide which data structure
you will use for the game. You need to tell the algorithm first and then need to write the code. Note: Some position
may be blank in the game। So your data structure should consider this condition also.
40. You are given an array [a1 To an] and we have to construct another array [b1 To bn] where bi = a1*a2*…*an/ai. you
are allowed to use only constant space and the time complexity is O(n). No divisions are allowed.
41. How do you put a Binary Search Tree in an array in a efficient manner. Hint :: If the node is stored at the ith
position and its children are at 2i and 2i+1(I mean level order wise)Its not the most efficient way.
42. How do you find out the fifth maximum element in an Binary Search Tree in efficient manner. Note: You should not
use use any extra space. i.e sorting Binary Search Tree and storing the results in an array and listing out the fifth
element.
43. Given a Data Structure having first n integers and next n chars. A = i1 i2 i3 … iN c1 c2 c3 … cN.Write an in-place
algorithm to rearrange the elements of the array ass A = i1 c1 i2 c2 … in cn
44. Given two sequences of items, find the items whose absolute number increases or decreases the most when comparing
one sequence with the other by reading the sequence only once.
45. Given That One of the strings is very very long , and the other one could be of various sizes. Windowing will
result in O(N+M) solution but could it be better? May be NlogM or even better?
46. How many lines can be drawn in a 2D plane such that they are equidistant from 3 non-collinear points?
47. Let’s say you have to construct Google maps from scratch and guide a person standing on Gateway of India (Mumbai)
to India Gate(Delhi). How do you do the same?
48. Given that you have one string of length N and M small strings of length L. How do you efficiently find the
occurrence of each small string in the larger one?
49. Given a binary tree, programmatically you need to prove it is a binary search tree.
50. You are given a small sorted list of numbers, and a very very long sorted list of numbers – so long that it had to
be put on a disk in different blocks. How would you find those short list numbers in the bigger one?
51. Suppose you have given N companies, and we want to eventually merge them into one big company. How many ways are
theres to merge?
52. Given a file of 4 billion 32-bit integers, how to find one that appears at least twice?
53. Write a program for displaying the ten most frequent words in a file such that your program should be efficient
in all complexity measures.
54. Design a stack. We want to push, pop, and also, retrieve the minimum element in constant time.
55. Given a set of coin denominators, find the minimum number of coins to give a certain amount of change.
56. Given an array,
i) find the longest continuous increasing subsequence.
ii) find the longest increasing subsequence.
57. Suppose we have N companies, and we want to eventually merge them into one big company. How many ways are there to
merge?
58. Write a function to find the middle node of a single link list.
59. Given two binary trees, write a compare function to check if they are equal or not. Being equal means that they
have the same value and same structure.
60. Implement put/get methods of a fixed size cache with LRU replacement algorithm.
61. You are given with three sorted arrays ( in ascending order), you are required to find a triplet ( one element
from each array) such that distance is minimum. Distance is defined like this : If a[i], b[j] and c[k] are three
elements then distance=max(abs(a[i]-b[j]),abs(a[i]-c[k]),abs(b[j]-c[k]))”
Please give a solution in O(n) time complexity
62. How does C++ deal with constructors and deconstructors of a class and its child class?
63. Write a function that flips the bits inside a byte (either in C++ or Java). Write an algorithm that take a list
of n words, and an integer m, and retrieves the mth most frequent word in that list.
64. What’s 2 to the power of 64?
65. Given that you have one string of length N and M small strings of length L. How do you efficiently find the
occurrence of each small string in the larger one?
66. How do you find out the fifth maximum element in an Binary Search Tree in efficient manner.
67. Suppose we have N companies, and we want to eventually merge them into one big company. How many ways are there
to merge?
68. There is linked list of millions of node and you do not know the length of it. Write a function which will return
a random number from the list.
69. You need to check that your friend, Bob, has your correct phone number, but you cannot ask him directly. You must
write a the question on a card which and give it to Eve who will take the card to Bob and return the answer to you.
What must you write on the card, besides the question, to ensure Bob can encode the message so that Eve cannot read
your phone number?
70. How long it would take to sort 1 trillion numbers? Come up with a good estimate.
71. Order the functions in order of their asymptotic performance: 1) 2^n 2) n^100 3) n! 4) n^n
72. There are some data represented by(x,y,z). Now we want to find the Kth least data. We say (x1, y1, z1) > (x2, y2, z2)
when value(x1, y1, z1) > value(x2, y2, z2) where value(x,y,z) = (2^x)*(3^y)*(5^z). Now we can not get it by calculating
value(x,y,z) or through other indirect calculations as lg(value(x,y,z)). How to solve it?
73. How many degrees are there in the angle between the hour and minute hands of a clock when the time is a quarter
past three?
74. Given an array whose elements are sorted, return the index of a the first occurrence of a specific integer.
Do this in sub-linear time. I.e. do not just go through each element searching for that element.
75. Given two linked lists, return the intersection of the two lists: i.e. return a list containing only the elements
that occur in both of the input lists.
76. What’s the difference between a hashtable and a hashmap?
77. If a person dials a sequence of numbers on the telephone, what possible words/strings can be formed from the
letters associated with those numbers?
78. How would you reverse the image on an n by n matrix where each pixel is represented by a bit?
79. Create a fast cached storage mechanism that, given a limitation on the amount of cache memory, will ensure that
only the least recently used items are discarded when the cache memory is reached when inserting a new item. It
supports 2 functions: String get(T t) and void put(String k, T t).
80. Create a cost model that allows Google to make purchasing decisions on to compare the cost of purchasing more RAM
memory for their servers vs. buying more disk space.
81. Design an algorithm to play a game of Frogger and then code the solution. The object of the game is to direct
a frog to avoid cars while crossing a busy road. You may represent a road lane via an array. Generalize the solution
for an N-lane road.
82. What sort would you use if you had a large data set on disk and a small amount of ram to work with?
83. What sort would you use if you required tight max time bounds and wanted highly regular performance.
84. How would you store 1 million phone numbers?
85. Design a 2D dungeon crawling game. It must allow for various items in the maze – walls, objects, and
computer-controlled characters. (The focus was on the class structures, and how to optimize the experience for the user
as s/he travels through the dungeon.)
86. What is the size of the C structure below on a 32-bit system? On a 64-bit?
struct foo {
char a;
char* b;
};
Google Interview: Software Engineer in Test
1. Efficiently implement 3 stacks in a single array.
2. Given an array of integers which is circularly sorted, how do you find a given integer.
3. Write a program to find depth of binary search tree without using recursion.
4. Find the maximum rectangle (in terms of area) under a histogram in linear time.
5. Most phones now have full keyboards. Before there there three letters mapped to a number button. Describe how you
would go about implementing spelling and word suggestions as people type.
6. Describe recursive mergesort and its runtime. Write an iterative version in C++/Java/Python.
7. How would you determine if someone has won a game of tic-tac-toe on a board of any size?
8. Given an array of numbers, replace each number with the product of all the numbers in the array except the number
itself *without* using division.
9. Create a cache with fast look up that only stores the N most recently accessed items.
10. How to design a search engine? If each document contains a set of keywords, and is associated with a numeric
attribute, how to build indices?
11. Given two files that has list of words (one per line), write a program to show the intersection.
12. What kind of data structure would you use to index annagrams of words? e.g. if there exists the word “top” in the
database, the query for “pot” should list that.
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