Author:

• Name: Ilya Kurdyukov
  Location: RU - Russian Federation (Russia)

Award: Most likely to count

To build:

    make all

To use:

    ./prog number .. 0 answer ..

Try:

    ./try.sh

Judges’ remarks:

How many arithmetic ways can we form numbers out of other numbers? The answer is a great deal. But to find the shortest mathematical expression: that is more of a challenge. To do that in only 1196 bytes of C code: that is impressive!

A fun challenge

Create an alternative form of prog.c (i.e., prog.alt.c) to allow the use of numbers in the interval [1, 2^31), or even the interval [1, 2^63).

The above fun challenge is still open. See the “Fun challenge Info” section for details.

Author’s remarks:

Magic Equations

Usage

    ./prog 7 77 777 0 2025 2026 2027 2028 2029
    (777 / 7 - 7) * (77 + 7) / 7 + 777 = 2025
    777 / 7 * 77 / 7 + 777 + 77 - 7 * 7 = 2026
    777 + 777 - 77 + 77 * 7 + 77 / 7 = 2027
    (77 + 7 / 7) * (7 + 7 + (77 + 7) / 7) = 2028
    77 * (7 + 7 + 77 / 7) + 777 / 7 - 7 = 2029

The program finds the shortest mathematical expression that uses numbers from the first list and +-*/ operators along with parentheses to represent numbers in the second list. Lists are separated by a zero.

Notes

• Numbers are limited in the interval [1, 2^15).
• The shortest in terms of string length (spaces are counted).
• This may not be the shortest possible for some numbers due to the limited search range.
• When compiled with -O3, the program calculates the result in about 4 seconds on an average PC. The computation time is almost independent of the length of the lists.

Primary files

• prog.c - entry source code
• Makefile - entry Makefile
• prog.orig.c - original source code
• try.sh - script to try entry

Secondary files

• 2025_kurdyukov.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• .date-range - copyright date range for this directory
• index.html - this web page

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