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](%%REPO_URL%%/2025/kurdyukov/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](../index.html#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.