# COMBINATION_LOCK 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.

### Languages:

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.

### Reference:

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.

### List of Routines:

• BICYCLE_LOCK finds the combination on a typical bicycle lock.
• COMBINATION_LOCK determines the combination of a lock.
• COMBINATION_NEXT generates lock combinations in lex order.
• GET_SEED returns a seed for the random number generator.
• I4_UNIFORM returns a scaled pseudorandom I4.
• I4VEC_EQ is true if two I4VECs are equal.
• I4VEC_PRINT prints an I4VEC.
• TIMESTAMP prints the current YMDHMS date as a time stamp.

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