Sample Problems

• count (277)

Previously Solved (latest first)

1. removing elements
2. symmetric difference
3. removing duplicate names from a comma-separated list
4. strict superset
5. split a list into a sublists

Knowledge Map

• basics
  • operation on primitive types
  • control flow statements
  • strings
• code organization
  • methods
  • object oriented programming
    • class hierarchies, interfaces and abstract classes
  • generic programming
  • functional programming
    • functions
    • functional streams
  • design patterns
• working with data
  • arrays
  • file processing
  • collections
• errorless code
• java internals
  • reflection
• additional instruments
  • essential standard classes
    • date and time
    • standard classes for computation
  • jdbc
  • regular expressions
• algorithms and data structures
  • algorithms
    • array algorithms
      • search algorithms

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operation on primitive types

topic	descriptions	num
distance	floating-point types	172
exponential expression	floating-point types	193
arithmethc expression	integer types and operations	155
desks	integer types and operations	163
difference of times	integer types and operations	161
good rest on vacation	integer types and operations	164
next even number	integer types and operations	162
how many nuts each squirrel will get	integer types and operations	156
reversing	integer types and operations	160
squirrels and nuts	integer types and operations	157
tens digit	integer types and operations	158
the sum of digits	integer types and operations	159
boys in a sports class	relational operators	167
check the sum	relational operators	169
exactly one parameter is positive	relational operators	166
groundhogs at a party	relational operators	170
is between	relational operators	168

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control flow statements

topic	descriptions	num
bus tour	branching statements	220
even or odd	branching statements	219
the integer barrier	branching statements	217
the sequence	branching statements	218
check a number if positive	conditional statement	201
chocolate	conditional statement	205
healthy sheep	conditional statement	1
interval	conditional statement	2
leap year	conditional statement	203
symmetrical number	conditional statement	202
the army of units	conditional statement	125
triangle	conditional statement	36
days of the week	switch expression	144
meteorological seasons	switch expression	143
months of the year	switch expression	147
direction	switch statement	223
floor-space of the room	switch statement	28
fromt string to number	switch statement	222
harry potter houses	switch statement	225
shape	switch statement	178
simple calculator	switch statement	224
test learners	switch statement	221
arithmetic average	the for-loop	211
fizz buzz	the for-loop	212
grades	the for-loop	215
maximum element divisible by four	the for-loop	214
numbers divisible by six	the for-loop	213
the product of numbers from a to b	the for-loop	216
size of parts	the for-loop	4
the sum of integers from a to b	the for-loop	210
the count of numbers divisible by n	the for-loop	179
collatz conjecture	the while and do-while loops	209
squares of natural numbers	the while and do-while loops	3
the smallest value	the while and do-while loops	207
the largest element of a sequence	the while and do-while loops	208
the sequence	the while and do-while loops	204
the sum of elements	the while and do-while loops	206

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strings

topic	descriptions	num
check burgs	string	151
check prefix ignoring the case	string	150
comparing strings ignoring whitespaces	string	153
extracting a substring	string	140
replace a with b	string	152
concat all strings without digits	stringbuilder	231
create email	stringbuilder	233
english alphabet	stringbuilder	232
love of big letters	stringbuilder	234
compression algorithm	processing strings	33
convert a date	processing strings	230
cutting out the middle of a string	processing strings	229
double characters	processing strings	228
euphonious word	processing strings	133
first occurrence of the word the	processing strings	139
gc characters	processing strings	149
generating passwords	processing strings	226
longest word	processing strings	134
lucky ticket	processing strings	37
move the first n characters	processing strings	227
number of occurrences	processing strings	142
palindrome	processing strings	135
parse url	processing strings	126
piece of alphabet	processing strings	136

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methods

topic	descriptions	num
adding values	arrays as parameters	240
inverse boolean flags	arrays as parameters	239
sorting numbers	arrays as parameters	238
parallelogram area	calling a method	141
composite number	declaring a method	5
number sign	declaring a method	6

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object oriented programming

topic	descriptions	num
managing speed in a car class	classes and objects, access control, access modifiers	251
student class with getters and constructor	classes and objects, access control, access modifiers	250
area of a circle	declaring functionalities with interfaces	262
polymorphic area calculator for shapes	declaring functionalities with interfaces	261
add new default method	default methods, interfaces and abstract classes, class hierarchies	266
implementing a greeting interface	default methods, interfaces and abstract classes, class hierarchies	264
implementing and extending color and shape interface	default methods, interfaces and abstract classes, class hierarchies	265
binary search	grouping classes with packages, classes and members, classes and objects	255
calculating package shipping cost by weight	grouping classes with packages, classes and members, classes and objects	254
creating instances	grouping classes with packages, classes and members, classes and objects	253
sorting arrays	grouping classes with packages, classes and members, classes and objects	256
clock simulation	instance methods	8
movie	multiple constructors	116
capture variables	nested classes, anonymous classes	131
managing a process	nested classes, anonymous classes	35
string reverser	nested classes, anonymous classes	263
pumpkin and canlde	nested classes, inner classes	148
days of week	other concepts, enumerations	132
balance management	other concepts, fields and methods in enum	182
robot control	other concepts, fields and methods in enum	181
publications	overriding methods, hiding and overriding	190
saying animals	overriding methods, hiding and overriding	191
shapes area	overriding methods, hiding and overriding	192
determining the taste of fruits using method overriding	overriding methods, polymorphism	260
publication subclasses	overriding methods, polymorphism	10
determining the taste of fruits using method overriding	polymorphism	260
implementing vehicle hierarchy with wheels	referencing subclass objects, class hierarchies	257
detail manufacturing	static members	114
bank account	the keyword super	235

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generic programming

topic	descriptions	num
correct the program	generic essentials, introduction to generic programming	174

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class hierarchies, interfaces and abstract classes

topic	descriptions	num
int binary operation	oop, interfaces and abstract classes, abstract class	11
implement compare to	oop, interfaces and abstract classes, comparable	43
implement comparing by additional fields	oop, interfaces and abstract classes, comparable	44
leaderboard	oop, interfaces and abstract classes, comparable	51
mutable geometric shapes	oop, interfaces and abstract classes, interface	17

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functions

topic	descriptions	num
chain of responsibilty	function composition	30
disjunct all	function composition	31
infinite number supplier	functional interfaces	121
lambda seven args	functional interfaces	19
filtering accounts	functional interfaces	119
ternary operator	functional interfaces	120
expression closure	lambda expressions	177
max of two integers	lambda expressions	176
check optional value	optional	42
create optional value	optional	41
sum up optional value	optional	198
the address book	optional	107

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functional streams

topic	descriptions	num
ascii art	collectors	93
product of squares	collectors	95
set average	collectors	94
a sorted stream	functional streams	77
count passwords	functional streams	74
finding max and min elemtents	functional streams	75
long ranges	functional streams	73
print elements of a stream	functional streams	76
a stream without zero	infinite stream	104
generating cats	infinite streams	101
powers of two	infinite streams	102
counting clicks	grouping collectors	100
grouping collectors	grouping collectors, theory	96
palindrome or not	grouping collectors	98
teeing collector	grouping collectors	97
total sum of transactions by each account	grouping collectors	99
count words without repetitions	map and flatmap	88
mapping countries	map and flatmap	84
mapping countries again	map and flatmap	85
match list and numbers	map and flatmap	83
maximum absolute value	map and flatmap	86
sorting absolute values	map and flatmap	87
calculating factorials	reduction methods	89
range quadratic sum	reduction methods	90
sum of divisors	reduction methods	91
bad words detecting	stream filtering	79
check if prime	stream filtering	80
numbers filtering	stream filtering	81
omitting long strings	stream filtering	82
the average salary	streams of primitives	103
secret codes	taking elements	105
sorting and skipping numbers	taking elements	106
sum of odd numbers	stream pipelines	108
ten most frequent words	stream pipelines	118
total number of employee	stream pipelines	109
total sum of cancelled transactions	stream pipelines	110
using streams many times	stream pipelines	117

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design patterns

topic	descriptions	num
forex broker	behavioral patterns, command	184
remote control	behavioral patterns, command	20
a new rockstar game	behavioral patterns, observer	175
rockstar games	behavioral patterns, observer	34
max and min	behavioral patterns, strategy	21
pick your team	behavioral patterns, strategy	180
build house	behavioral patterns, template method	26
career	behavioral patterns, template method	22
social networks	behavioral patterns, template method	27
template method	behavioral patterns, template method	24
template method v2	behavioral patterns, template method	25
static factory for time	creational patterns, encapsulating object creation	18
motor static factory	creational patterns, static factory idiom	23
list based implementation	data access object for jdbc	199
map based implementation	data access object for jdbc	200

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arrays

topic	descriptions	num
boxes	iterating over arrays	7
individual taxes	iterating over arrays	9
maximum product of adjacent elements	iterating over arrays	112
sum array elements greater than value	iterating over arrays	129
triples	iterating over arrays	45

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file processing

topic	descriptions	num
find the greatest number in file	reading files	241
count numbers in a file	reading files	242
sum of numbers in a file	reading files	243
count even numbers in a file	reading files	244
get year most increase population	reading files	245

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collections

topic	descriptions	num
concat positive numbers	arraylist	183
find the nearest number	arraylist	46
blacklist	collections framework overview	259
count and display element frequencies	collections framework overview	257
sorting the digits of an integer in ascending order	collections framework overview	252
squaring numbers	collections framework overview	258
messages comparator	comparator	67
most valuable items	comparator	69
multiple fields	comparator	72
odd and even	comparator	70
reverse sorting	comparator	71
sort users	comparator	68
backward indexes	list interface	29
companies	list interface	272
count value occurrences	list interface	32
filtering the list	list interface	270
find the middle element in a sequence	list interface	268
greek letters	list interface	269
split a list into a sublists	list interface	273
the longest string in the list	list interface	271
counting words	map interface	60
creating a tree map	map interface	57
diplaying pairs	map interface	59
getting submaps	map interface	185
kidnapper of ice cream	map interface	186
modifying a map	map interface	173
sherlock homes and the mystery of anagrams	map interface	58
sum of values	map interface	187
tricky submaps	map interface	113
value or min	map interface	188
removing duplicate names from a comma-separated list	set interface	275
removing elements	set interface	277
strict superset	set interface	274
symmetric difference	set interface	276

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errorless code

topic	descriptions	num
string modifier	debugger	63
bitwise and integers	debugging	64
cycles and iterations	debugging	78
divisors finding	debugging	62
converting and multiplying	exception handling	237
string to double	exception handling	236
avoid npe string	exception handling, npe	130
logging to debug	logback	115
proper arguments	mockito	66
return empty string	npe	111
test password	testing tools and libraries, parameterized test	50

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reflection

topic	descriptions	num
declared fields	reflection basics	145
field count	reflection basics	146

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date and time

topic	descriptions	num
count date time range match	comparing dates and times	92
dont be late again	comparing dates and time	15
instant to long	instant	247
min and max instant units	instant	248
print the correct instant unit	instant	249
find all mondays	localdate	165
last day of month	localdate	16
first and last day of month	localdate	127
similar date	localdate	12
ten days before	localdate	137
same time	localtime	13
merge datetime	localdatetime	138
subtracting hours adding minutes	localdatetime	128
the difference between duration units	period and duration classes	267
the difference between period units	period and duration classes	246

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standard classes for computation

topic	descriptions	num
average	big decimal	39
gold mining	big decimal	38
multiplication	big decimal	40
find the seed	random	14

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jdbc

topic	descriptions	num
dinosaurs and plants	jdbc, jdbc transactions	65

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regular expressions

topic	descriptions	num
card name validation and identification	string matches	48
check ip address	string matches	54
check the clock time	string matches	52
check the date	string matchees	53
safe password	string matches	49
check the essay	match results	189
email address	patterns and matchers	196
extracting big numbers from a text	patterns and matchers	56
find all passwords	patterns and matchers	55
find a word with given length	patterns and matchers	195
in the middle of a word	patterns and matchers	47
number parsing	patterns and matchers	122
start or end of word	patterns and matchers	197
illegal identifiers	regexes in programs	194
vehicle registration number	regexes in programs	154

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search algorithms

topic	descriptions	num
approximate search	algorithms, array algorithms, search algorithms	124
binary search count number of loops	algorithms, array algorithms, search algorithms	123
sort and search	algorithms, array algorithms, search algorithms	61

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