辅导案例-COSC 326 2020

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COSC 326 2020 Summer School Étude 8
Arithmetic
A common sort of puzzle or problem one sees in newspapers, particularly at the be-
ginning of each year goes along the lines of “make up a formula whose value is 2018,
using the numbers 1 through 10 in that order”. Of course the rules of the game are
never entirely clear - in particular whether brackets are allowed, and what operations
are permissible.
In this étude we’ll look at a simplified model. The only operations allowed are + and
× and brackets are not permitted. However, we’ll consider both ‘proper’ order of op-
erations where
1 + 2× 3 = 7
and ‘left to right’ where
1 + 2× 3 =LR 9.
Task
Input from stdin will be a sequence of scenarios. Each scenario is exactly two lines.
The first line is the numbers to use, and the second line consists of a target value, fol-
lowed by a space, followed by the character N or the character L indicating whether
normal order of operations, or left to right order is to be assumed.
The output for a scenario should be a character representing the order used, then
the target value, and finally an expression of the required value (using the character
* for multiplication, and with spaces before and after each operation), or the word
impossible.
Example
Input:
1 2 3
7 N
1 2 3
9 L
1 2 3
100 N
Output:
N 7 1 + 2 * 3
L 9 1 + 2 * 3
N 100 impossible
COSC 326 2020 Summer School Étude 8
Relates to Objectives
2.1-3 2.5 2.10 3.4 3.5
(2 points, Individual)
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