Tasks Details
medium
1.
DoubleHanoi
Find the maximum number of disks that can be placed on two rods. The disks should be in decreasing order of size on the first rod and in increasing order of size on the second rod.
Task Score
100%
Correctness
100%
Performance
100%
You are given N disks and two rods, each with one initial disk.
On the left rod, disks can be placed in decreasing order of size (smaller disks on top of bigger ones). On the right rod, disks can be placed in increasing order of size (bigger disks on top of smaller ones). Note that it is not permissible to place two disks of equal size on top of each other. The initial disks cannot be moved.
Write a function:
def solution(a, l, r)
that, given an array A of integers representing the sizes of the N disks and two integers L and R representing the size of the initial disks on the left and right rods respectively, returns the maximum number of disks from A that can be placed on the rods while satisfying the rules presented above.
Examples:
1. Given A = [2, 3, 3, 4], L = 3 and R = 1, your function should return 3, since only three disks can be placed on the rods. Note that the disk of size 2 can be placed on either the left rod or the right rod.
2. Given A = [1, 4, 5, 5], L = 6 and R = 4, your function should return 4.
3. Given A = [5, 2, 5, 2], L = 8 and R = 1, your function should return 4.
4. Given A = [1, 5, 5], L = 2 and R = 4, your function should return 2.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [1..50,000];
- each element of array A is an integer within the range [1..1,000,000,000];
- L and R are integers within the range [1..1,000,000,000].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Ruby
Time spent on task 46 minutes
Notes
not defined yet
Code: 19:02:03 UTC,
java,
autosave
Code: 19:20:36 UTC,
rb,
autosave
Code: 19:21:05 UTC,
rb,
autosave
Code: 19:21:22 UTC,
rb,
autosave
Code: 19:21:33 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
a.sort!
count = 0
count_started = false
a.each_with_index do |val,i|
if count_started and val != a[i-1]
count += 1
next
end
if val
end
end
Code: 19:21:44 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
a.sort!
count = 0
count_started = false
a.each_with_index do |val,i|
if count_started and val != a[i-1]
count += 1
next
end
if val >
end
end
Code: 19:23:22 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
a.sort!
count = 0
count_started = false
a.each_with_index do |val,i|
if count_started and val != a[i-1]
count += 1
next
end
if val >
end
end
Code: 19:23:33 UTC,
rb,
autosave
Code: 19:27:16 UTC,
rb,
autosave
Code: 19:27:54 UTC,
rb,
autosave
Code: 19:28:05 UTC,
rb,
autosave
Code: 19:28:16 UTC,
rb,
autosave
Code: 19:28:28 UTC,
rb,
autosave
Code: 19:28:40 UTC,
rb,
autosave
Code: 19:29:03 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val]
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:29:17 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:29:30 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:30:00 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val]
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:30:13 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:36:12 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:36:34 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:36:52 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:37:10 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
end
Code: 19:37:28 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
count
end
Code: 19:37:33 UTC,
rb,
verify,
result: Failed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] += 1
next
end
end
count
end
Analysis
expand all
Example tests
1.
0.044 s
RUNTIME ERROR,
tested program terminated with exit code 1
stderr:
exec.rb:21:in `block in solution': undefined method `+' for nil:NilClass (NoMethodError) from exec.rb:8:in `each' from exec.rb:8:in `solution' from exec.rb:139:in `<main>'
1.
0.044 s
RUNTIME ERROR,
tested program terminated with exit code 1
stderr:
exec.rb:21:in `block in solution': undefined method `+' for nil:NilClass (NoMethodError) from exec.rb:8:in `each' from exec.rb:8:in `solution' from exec.rb:139:in `<main>'
1.
0.044 s
RUNTIME ERROR,
tested program terminated with exit code 1
stderr:
exec.rb:21:in `block in solution': undefined method `+' for nil:NilClass (NoMethodError) from exec.rb:8:in `each' from exec.rb:8:in `solution' from exec.rb:139:in `<main>'
1.
0.044 s
RUNTIME ERROR,
tested program terminated with exit code 1
stderr:
exec.rb:21:in `block in solution': undefined method `+' for nil:NilClass (NoMethodError) from exec.rb:8:in `each' from exec.rb:8:in `solution' from exec.rb:139:in `<main>'
Code: 19:37:58 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:38:03 UTC,
rb,
verify,
result: Passed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Analysis
Code: 19:41:04 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:41:36 UTC,
rb,
verify,
result: Passed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Analysis
Code: 19:42:52 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
next
end
end
count
end
Code: 19:43:03 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
next
end
end
count
end
Code: 19:43:25 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:43:56 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:44:10 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] and hash[val] >= 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:44:21 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] and hash[val] == 1
hash[val] += 1
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:44:33 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l) and hash[val].nil?
count += 1
hash[val] = 1
next
end
end
count
end
Code: 19:44:43 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Code: 19:45:13 UTC,
rb,
verify,
result: Passed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Analysis
Code: 19:45:26 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Code: 19:45:49 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2 and val > r and val < l
count += 1
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Code: 19:45:59 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2 and val > r and val < l
count += 1
next
end
if val > r or val < l
count += 1
next
end
end
count
end
Code: 19:46:03 UTC,
rb,
verify,
result: Failed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2 and val > r and val < l
count += 1
next
end
if val > r or val < l
count += 1
next
end
end
count
end
Analysis
expand all
Example tests
1.
0.044 s
WRONG ANSWER,
got 4 expected 3
1.
0.044 s
OK
1.
0.044 s
OK
1.
0.044 s
WRONG ANSWER,
got 3 expected 2
Code: 19:46:30 UTC,
rb,
autosave
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Code: 19:46:38 UTC,
rb,
verify,
result: Passed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Analysis
Code: 19:47:28 UTC,
rb,
verify,
result: Passed
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Analysis
Code: 19:47:31 UTC,
rb,
final,
score:
100
# you can write to stdout for debugging purposes, e.g.
# puts "this is a debug message"
def solution(a, l, r)
# write your code in Ruby 2.2
count = 0
hash = {}
a.each do |val|
hash[val] = 0 if hash[val].nil?
hash[val] += 1
if hash[val] > 2
next
end
if hash[val] == 2
if val > r and val < l
count += 1
end
next
end
if (val > r or val < l)
count += 1
next
end
end
count
end
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N*log(N)) or O(N)
expand all
Correctness tests
1.
0.044 s
OK
2.
0.044 s
OK
3.
0.044 s
OK
1.
0.044 s
OK
2.
0.044 s
OK
1.
0.044 s
OK
2.
0.044 s
OK
1.
0.044 s
OK
2.
0.044 s
OK
3.
0.044 s
OK
4.
0.044 s
OK
1.
0.044 s
OK
2.
0.044 s
OK
3.
0.044 s
OK
4.
0.044 s
OK
5.
0.044 s
OK
6.
0.044 s
OK
small_every_value_occurs_more_than_once
Small random tests, every value occurs at least twice. N = 100.
Small random tests, every value occurs at least twice. N = 100.
✔
OK
1.
0.044 s
OK
2.
0.044 s
OK
3.
0.044 s
OK
4.
0.044 s
OK
1.
0.044 s
OK
2.
0.044 s
OK
3.
0.044 s
OK
4.
0.044 s
OK
expand all
Correctness/performance tests
1.
0.052 s
OK
2.
0.052 s
OK
3.
0.052 s
OK
4.
0.056 s
OK
5.
0.052 s
OK
6.
0.056 s
OK
1.
0.076 s
OK
2.
0.076 s
OK
3.
0.072 s
OK
4.
0.088 s
OK
5.
0.092 s
OK
6.
0.088 s
OK
expand all
Performance tests
1.
0.056 s
OK
2.
0.056 s
OK
3.
0.056 s
OK
4.
0.056 s
OK
5.
0.056 s
OK
6.
0.056 s
OK
1.
0.096 s
OK
2.
0.096 s
OK
3.
0.096 s
OK
4.
0.092 s
OK