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:
int solution(vector<int> &A, int L, int 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 C++
Time spent on task 14 minutes
Notes
not defined yet
Code: 20:08:08 UTC,
java,
autosave
Code: 20:08:14 UTC,
cpp,
autosave
Code: 20:15:12 UTC,
cpp,
autosave
Code: 20:15:27 UTC,
cpp,
autosave
Code: 20:15:46 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A, int L, int R) {
sort( begin(v), end(v));
for ( x : v ){
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:16:02 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A, int L, int R) {
sort( begin(v), end(v));
for ( x : v ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:16:03 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A, int L, int R) {
sort( begin(v), end(v));
for ( x : v ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Compile error
func.cpp: In function 'int solution(std::vector<int>&, int, int)':
func.cpp:8:17: error: 'v' was not declared in this scope
sort( begin(v), end(v));
^
func.cpp:8:27: error: 'sort' was not declared in this scope
sort( begin(v), end(v));
^
func.cpp:10:13: error: found ':' in nested-name-specifier, expected '::'
for ( x : v ){
^
func.cpp:10:11: error: 'x' has not been declared
for ( x : v ){
^
func.cpp:14:1: error: expected primary-expression before '}' token
}
^
func.cpp:14:1: error: expected ';' before '}' token
func.cpp:14:1: error: expected primary-expression before '}' token
func.cpp:14:1: error: expected ')' before '}' token
func.cpp:14:1: error: expected primary-expression before '}' token
func.cpp:14:1: warning: no return statement in function returning non-void [-Wreturn-type]
Code: 20:16:19 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A));
for ( x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Compile error
func.cpp: In function 'int solution(std::vector<int>&, int, int)':
func.cpp:8:27: error: 'sort' was not declared in this scope
sort( begin(A), end(A));
^
func.cpp:10:13: error: found ':' in nested-name-specifier, expected '::'
for ( x : A ){
^
func.cpp:10:11: error: 'x' has not been declared
for ( x : A ){
^
func.cpp:14:1: error: expected primary-expression before '}' token
}
^
func.cpp:14:1: error: expected ';' before '}' token
func.cpp:14:1: error: expected primary-expression before '}' token
func.cpp:14:1: error: expected ')' before '}' token
func.cpp:14:1: error: expected primary-expression before '}' token
func.cpp:14:1: warning: no return statement in function returning non-void [-Wreturn-type]
Code: 20:16:27 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A));
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Compile error
func.cpp: In function 'int solution(std::vector<int>&, int, int)':
func.cpp:8:27: error: 'sort' was not declared in this scope
sort( begin(A), end(A));
^
func.cpp:14:1: warning: no return statement in function returning non-void [-Wreturn-type]
}
^
Code: 20:16:34 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A));
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:16:41 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A));
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
expand all
Example tests
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 3
stdout:
2,3,3,4,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 4
stdout:
1,4,5,5,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 4
stdout:
2,2,5,5,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 2
stdout:
1,5,5,
Code: 20:17:58 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), gr);
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:18:04 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>);
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Compile error
func.cpp: In function 'int solution(std::vector<int>&, int, int)':
func.cpp:8:41: error: expected primary-expression before ')' token
sort( begin(A), end(A), greater<int>);
^
func.cpp:14:1: warning: no return statement in function returning non-void [-Wreturn-type]
}
^
Code: 20:18:14 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Analysis
expand all
Example tests
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 3
stdout:
4,3,3,2,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 4
stdout:
5,5,4,1,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 4
stdout:
5,5,2,2,
1.
0.001 s
WRONG ANSWER,
got 6300864 expected 2
stdout:
5,5,1,
Code: 20:18:30 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:18:43 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int L;
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:18:54 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int L;
vector<int> B;
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:19:17 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
vector<int> B;
for ( auto x : A ){
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:19:47 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result =
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
}
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:20:15 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
cout << x << ",";
}
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:20:32 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:20:47 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(b) );
return result;
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:21:08 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(b) );
for ( auto x : B ){
if ( x > lastRight )
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Code: 20:21:25 UTC,
cpp,
verify,
result: Failed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(b) );
for ( auto x : B ){
if ( x > lastRight ){
lastRight = x;
result++;
}
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Compile error
func.cpp: In function 'int solution(std::vector<int>&, int, int)':
func.cpp:23:25: error: 'b' was not declared in this scope
sort( begin(B), end(b) );
^
Code: 20:21:36 UTC,
cpp,
verify,
result: Passed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(B) );
for ( auto x : B ){
if ( x > lastRight ){
lastRight = x;
result++;
}
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Code: 20:21:45 UTC,
cpp,
verify,
result: Passed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(B) );
for ( auto x : B ){
if ( x > lastRight ){
lastRight = x;
result++;
}
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Analysis
Code: 20:21:49 UTC,
cpp,
final,
score:
100
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
#include<algorithm>
int solution(vector<int> &A, int L, int R) {
sort( begin(A), end(A), greater<int>());
int lastLeft = L;
int lastRight = R;
int result = 0;
vector<int> B;
for ( auto x : A ){
if ( x < lastLeft ){
lastLeft = x;
result++;
} else {
B.push_back(x);
}
}
sort( begin(B), end(B) );
for ( auto x : B ){
if ( x > lastRight ){
lastRight = x;
result++;
}
}
return result;
// write your code in C++14 (g++ 6.2.0)
}
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N*log(N)) or O(N)
expand all
Correctness tests
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
5.
0.001 s
OK
6.
0.001 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.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
expand all
Correctness/performance tests
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
5.
0.001 s
OK
6.
0.001 s
OK
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.004 s
OK
4.
0.004 s
OK
5.
0.004 s
OK
6.
0.004 s
OK
expand all
Performance tests
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.004 s
OK
4.
0.004 s
OK
5.
0.004 s
OK
6.
0.004 s
OK
1.
0.008 s
OK
2.
0.008 s
OK
3.
0.008 s
OK
4.
0.008 s
OK