public/subjects/rpn/README.md

rpn

Instructions

Write a program which takes a string containing an equation written in Reverse Polish Notation (RPN). It should evaluate the equation, and print the result on the standard output followed by a newline ('\n').

Reverse Polish Notation is a mathematical notation in which every operator follows all of its operands. In RPN, every operator encountered evaluates the previous 2 operands, and the result of this operation then becomes the first of the two operands for the subsequent operator. Operands and operators must be spaced by at least one space.

• If the string is not valid, or if there is not exactly one argument, Error must be printed on the standard output followed by a newline.
• If the string has extra spaces it is still considered valid.

The following operators must be implemented : +, -, *, /, and %.

All the given operands must fit in a i64.

Examples of formulas converted in RPN:

3 + 4 >> 3 4 +

((1 * 2) * 3) - 4 >> 1 2 * 3 * 4 - or 3 1 2 * * 4 -

50 * (5 - (10 / 9)) >> 5 10 9 / - 50 *

Here is how to evaluate a formula in RPN:

1 2 * 3 * 4 -
2 3 * 4 -
6 4 -
2

Or:

3 1 2 * * 4 -
3 2 * 4 -
6 4 -
2

For receiving arguments from the command line you should use something like:

    fn main() {
        let args: Vec<String> = std::env::args().collect();

        rpn(&args[1]);
    }

Usage

$ cargo run "1 2 * 3 * 4 +"
10
$ cargo run "1 2 3 4 +"
Error
$ cargo run ""
Error
$ cargo run "     1      3 * 2 -"
1
$ cargo run "     1      3 * ksd 2 -"
Error