Key Information

The challenge is finished.

Challenge Overview

Important Links

  • Submission-Review You can find your submissions artifacts here. Artifacts will contain output.txt's for both example test cases and provisional test cases with stdout/stderr and individual test case scores.
  • Other Details: For other details like Processing Server Specifications, Submission Queue, Example Test Cases Execution.


You are given a sequence S containing N numbers in the range [0, K). Your task is to sort this sequence into monotonically increasing order, in a way that incurs the smallest penalty. You are allowed to select any contiguous sub-sequence of numbers and reverse their order. Formally, if the sub-sequence is (S[i], S[i+1], ..., S[k-1], S[k]), where 0 <= i < k < N, then its reversal is (S[k], S[k-1], ..., S[i+1], S[i]). The penalty incurred by this reversal is floor[(k-i+1)^X], where X is a given penalty parameter. Your task is to minimize the total penalty incurred by all the reversals.

Here is a solution for seed=1 with N=10, K=5 and X=1.0. The sub-sequences being reversed are shown inside brackets:

Input sequence:
1 1 1 0 3 0 1 1 2 4

Move 1, move score 2, total score 2
1 1 1 0 (3 0) 1 1 2 4

Move 2, move score 3, total score 5
1 1 1 0 0 (3 1 1) 2 4

Move 3, move score 5, total score 10
(1 1 1 0 0) 1 1 3 2 4

Move 4, move score 2, total score 12
0 0 1 1 1 1 1 (3 2) 4

Sorted sequence:
0 0 1 1 1 1 1 2 3 4


Your code will receive as input the following values, each on a separate line:
  • N, the length of the sequence.
  • K, the maximum number of distinct values in the sequence.
  • X, the penalty parameter.
This is followed by N lines representing the sequence to be sorted. Each line will contain a single integer in the range [0, K).


Your code should write to output the following:
  • On the first line, R, the number of reversal to perform.
  • R lines, each representing a single reversal. The format should be "i k" (without the quotes), where i is the starting index and k is the ending index of the reversal (i < k, both 0-based).


The scorer will compute the total penalty incurred by the reversals.

If your return was invalid, then your raw score on this test case will be -1. Possible reasons include:
  • Using more than floor[(N*N)/2] reversals.
  • Using invalid characters or incorrectly formatted reversals.
  • Using indices that are out of bounds.
If your raw score for a test case is negative then your normalized score for that test case is 0. Otherwise, your normalized score for each test case is MIN/YOUR, where YOUR is your raw score and MIN is the smallest positive raw score currently obtained on this test case (considering only the last submission from each competitor). Finally, the sum of all your test scores is normalized to 100.

Test Case Generation

Please look at the generate() method in visualizer's source code for the exact details about test case generation. Each test case is generated as follows:
  • The length of the sequence N is chosen between 10 and 1000, inclusive.
  • The maximum number of distinct values K is chosen between 2 and N, inclusive.
  • The penalty parameter X is chosen between 0.0 and 3.0, inclusive.
  • Generate N sequence values, each in the range [0, K).
  • All values are chosen uniformly at random.


  • The time limit is 10 seconds per test case (this includes only the time spent in your code). The memory limit is 1024 megabytes.
  • The compilation time limit is 30 seconds.
  • There are 10 example test cases and 100 full submission (provisional) test cases. There will be 2000 test cases in the final testing.
  • The match is rated.

Languages Supported

C#, Java, C++ and Python

Submission Format

Your submission must be a single ZIP file not larger than 500 MB, with your source code only.
Please Note: Please zip only the file. Do not put it inside a folder before zipping, you should directly zip the file.

Make sure you name your Source Code file as ReversalSort.<appropriate extension>


Here are example solutions for different languages, modified to be executed with the visualizer. You may modify and submit these example solutions.


An offline tester is available below. You can use it to test/debug your solution locally. You can also check its source code for an exact implementation of test case generation and score calculation. You can also find links to useful information and sample solutions in several languages.



In order to use the offline tester/visualizer tool for testing your solution locally, you'll have to include in your solution the main method that interacts with the tester/visualizer via reading data from standard input and writing data to standard output.

To run the tester with your solution, you should run:

java -jar ReversalSort.jar -exec "<command>" -seed <seed>

Here, <command> is the command to execute your program, and <seed> is seed for test case generation.
If your compiled solution is an executable file, the command will be the full path to it, for example, "C:\TopCoder\ReversalSort.exe" or "~/topcoder/ReversalSort".
In case your compiled solution is to be run with the help of an interpreter, for example, if you program in Java, the command will be something like "java -cp C:\TopCoder ReversalSort".

Additionally you can use the following options:
  • -seed <seed> Sets the seed used for test case generation, default is seed 1.
  • -debug Print debug information.
  • -N <N> Sets a custom sequence length.
  • -K <K> Sets a custom maximum number of distinct values.
  • -X <X> Sets a custom penalty parameter.
Custom parameters also accept ranges. For example -N 20,30 makes the sequence length to be randomly chosen between 20 and 30, inclusive. Finally, you can print any debug information of your solution to standard error, and it will be forwarded to the standard out of the tester.

Marathon local testers also have other options, including running a range of seeds with a single command, running more than one seed at time (multiple threads), controlling time limit, saving input/output/error and loading solution from a file. The usage of these other options are described here.