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:
class Solution { public int solution(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 Java 21
Time spent on task 25 minutes
Notes
not defined yet
Code: 22:50:39 UTC,
java,
autosave
Code: 22:59:46 UTC,
java,
autosave
Code: 23:00:12 UTC,
java,
autosave
Code: 23:02:07 UTC,
java,
autosave
Code: 23:02:31 UTC,
java,
autosave
Code: 23:02:44 UTC,
java,
autosave
Code: 23:02:55 UTC,
java,
verify,
result: Failed
Analysis
expand all
Example tests
1.
0.004 s
WRONG ANSWER,
got 0 expected 3
1.
0.008 s
WRONG ANSWER,
got 0 expected 4
1.
0.008 s
WRONG ANSWER,
got 0 expected 4
1.
0.004 s
WRONG ANSWER,
got 0 expected 2
expand all
User tests
1.
0.001 s
RUNTIME ERROR,
invalid input, unexpected ']', expecting integer
User test case 1:
[9,7,5,2,6],5,1
Code: 23:03:15 UTC,
java,
autosave
Code: 23:03:16 UTC,
java,
verify,
result: Failed
Analysis
expand all
Example tests
1.
0.004 s
WRONG ANSWER,
got 0 expected 3
1.
0.004 s
WRONG ANSWER,
got 0 expected 4
1.
0.008 s
WRONG ANSWER,
got 0 expected 4
1.
0.008 s
WRONG ANSWER,
got 0 expected 2
User test case 1:
[[9, 7, 5, 2, 6], 5, 1]
Code: 23:05:09 UTC,
java,
autosave
Code: 23:05:21 UTC,
java,
autosave
Code: 23:07:59 UTC,
java,
autosave
Code: 23:08:23 UTC,
java,
autosave
Code: 23:08:46 UTC,
java,
autosave
// you can also use imports, for example:
// import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap
return 0;
}
}
Code: 23:08:57 UTC,
java,
autosave
// you can also use imports, for example:
// import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
return 0;
}
}
Code: 23:09:07 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
return 0;
}
}
Code: 23:09:30 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
if(A)
return 0;
}
}
Code: 23:09:54 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int numbersUserd = 0;
for(int )
return 0;
}
}
Code: 23:10:08 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int numbersUserd = 0;
for(int disks: A){
}
return 0;
}
}
Code: 23:10:18 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int numbersUsed = 0;
for(int disks: A){
}
return numbersUsed;
}
}
Code: 23:10:28 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disks: A){
}
return disksUsed;
}
}
Code: 23:10:38 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disks: A){
if()
}
return disksUsed;
}
}
Code: 23:10:57 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && )
}
return disksUsed;
}
}
Code: 23:11:07 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get())
}
return disksUsed;
}
}
Code: 23:11:26 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get(disk)==null){
}
}
return disksUsed;
}
}
Code: 23:11:36 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get(disk)==null){
leftRod.set(,)
}
}
return disksUsed;
}
}
Code: 23:11:49 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get(disk)==null){
leftRod.set(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:11:59 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:12:14 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk>L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}
if(disk>R && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:12:26 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}
if(disk>R && leftRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:12:37 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}
if(disk>R && leftRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:12:47 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && leftRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:13:04 UTC,
java,
verify,
result: Failed
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && leftRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis
expand all
Example tests
1.
0.012 s
WRONG ANSWER,
got 4 expected 3
1.
0.008 s
WRONG ANSWER,
got 3 expected 4
1.
0.004 s
WRONG ANSWER,
got 2 expected 4
1.
0.004 s
WRONG ANSWER,
got 3 expected 2
Code: 23:13:28 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rigRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:13:31 UTC,
java,
verify,
result: Passed
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis
Code: 23:14:09 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:14:23 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:14:27 UTC,
java,
verify,
result: Passed
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis
User test case 1:
[[3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3], 3, 3]
Code: 23:14:41 UTC,
java,
autosave
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Code: 23:14:48 UTC,
java,
verify,
result: Passed
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis
User test case 1:
[[3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 1, 1, 3], 3, 3]
Code: 23:14:57 UTC,
java,
verify,
result: Passed
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis
User test case 1:
[[3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 1, 1, 3], 3, 3]
Code: 23:15:02 UTC,
java,
final,
score:
100
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A, int L, int R) {
HashMap<Integer,Integer> leftRod = new HashMap<Integer,Integer>();
HashMap<Integer,Integer> rightRod = new HashMap<Integer,Integer>();
int disksUsed = 0;
for(int disk: A){
if(disk<L && leftRod.get(disk)==null){
leftRod.put(disk,1);
disksUsed++;
}else if(disk>R && rightRod.get(disk)==null){
rightRod.put(disk,1);
disksUsed++;
}
}
return disksUsed;
}
}
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N*log(N)) or O(N)
expand all
Correctness tests
1.
0.012 s
OK
2.
0.012 s
OK
3.
0.012 s
OK
1.
0.012 s
OK
2.
0.012 s
OK
1.
0.012 s
OK
2.
0.012 s
OK
1.
0.008 s
OK
2.
0.012 s
OK
3.
0.012 s
OK
4.
0.012 s
OK
1.
0.012 s
OK
2.
0.012 s
OK
3.
0.012 s
OK
4.
0.012 s
OK
5.
0.012 s
OK
6.
0.008 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.
0.012 s
OK
2.
0.012 s
OK
3.
0.008 s
OK
4.
0.012 s
OK
1.
0.012 s
OK
2.
0.008 s
OK
3.
0.008 s
OK
4.
0.012 s
OK
expand all
Correctness/performance tests
1.
0.036 s
OK
2.
0.028 s
OK
3.
0.032 s
OK
4.
0.052 s
OK
5.
0.052 s
OK
6.
0.048 s
OK
1.
0.136 s
OK
2.
0.108 s
OK
3.
0.136 s
OK
4.
0.240 s
OK
5.
0.240 s
OK
6.
0.244 s
OK
expand all
Performance tests
1.
0.068 s
OK
2.
0.068 s
OK
3.
0.064 s
OK
4.
0.044 s
OK
5.
0.044 s
OK
6.
0.044 s
OK
1.
0.304 s
OK
2.
0.300 s
OK
3.
0.176 s
OK
4.
0.176 s
OK