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#!/usr/bin/env perl
# Author: Steven Wilson
# Date: 2019-12-16
# Week: 039
# TASK #2
# Contributed by Andrezgz
# Write a script to demonstrate Reverse Polish notation(RPN). Checkout
# the wiki page for more information about RPN.
# https://en.wikipedia.org/wiki/Reverse_Polish_notation
use strict;
use warnings;
use Test::More tests => 2;
my %dt = (
'+' => sub { $_[0] + $_[1] },
'-' => sub { $_[0] - $_[1] },
'x' => sub { $_[0] * $_[1] },
'/' => sub { $_[0] / $_[1] },
);
ok( evaluate("1 2 +") == 3 );
ok( evaluate("15 7 1 1 + - / 3 x 2 1 1 + + -") == 5 );
# for each token in the postfix expression:
# if token is an operator:
# operand_2 ← pop from the stack
# operand_1 ← pop from the stack
# result ← evaluate token with operand_1 and operand_2
# push result back onto the stack
# else if token is an operand:
# push token onto the stack
# result ← pop from the stack
sub evaluate {
my $expression = shift;
my @expression = split " ", $expression;
my @stack = ();
for my $token (@expression) {
if ( $token =~ /\d+/ ) {
push @stack, $token;
}
else {
my $operand_2 = pop @stack;
my $operand_1 = pop @stack;
my $result = $dt{$token}->( $operand_1, $operand_2 );
push @stack, $result;
}
}
return pop @stack;
}
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