The Combination Lock Problem

COMBINATION_LOCK is a FORTRAN90 program which simulates the process of determining the combination of a lock.

This program demonstrates the method of exhaustive search, that is, it searches for an answer by trying every possibility. This requires a way of logically ordering the possibilities.


The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.


COMBINATION_LOCK is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

BICYCLE_LOCK, a FORTRAN90 library which simulates the process of determining the secret combination of a bicycle lock, an integer between 000 and 999.

CHANGE_MAKING, a FORTRAN90 library which considers the change making problem, in which a given sum is to be formed using coins of various denominations.

COMBO, a FORTRAN90 library which includes many combinatorial routines.

KNAPSACK_01, a FORTRAN90 library which uses brute force to solve small versions of the 0/1 knapsack problem;

PARTITION_PROBLEM, a FORTRAN90 library which seeks solutions of the partition problem, splitting a set of integers into two subsets with equal sum.

SATISFY, a FORTRAN90 program which demonstrates, for a particular circuit, an exhaustive search for solutions of the circuit satisfiability problem.

SUBSET, a FORTRAN90 library which enumerates combinations, partitions, subsets, index sets, and other combinatorial objects.

SUBSET_SUM, a FORTRAN90 library which seeks solutions of the subset sum problem.

TSP_BRUTE, a FORTRAN90 program which reads a file of city-to-city distances and solves the traveling salesperson problem, using brute force.


  1. Donald Kreher, Douglas Simpson,
    Combinatorial Algorithms,
    CRC Press, 1998,
    ISBN: 0-8493-3988-X,
    LC: QA164.K73.
  2. Silvano Martello, Paolo Toth,
    Knapsack Problems: Algorithms and Computer Implementations,
    Wiley, 1990,
    ISBN: 0-471-92420-2,
    LC: QA267.7.M37.

Source Code:

Examples and Tests:

List of Routines:

You can go up one level to the FORTRAN90 source codes.

Last modified on 13 May 2012.