Created
April 19, 2020 16:15
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Reverse Polish Notation
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| import java.util.LinkedList; | |
| import java.util.List; | |
| import java.util.regex.Pattern; | |
| import java.util.stream.Collectors; | |
| import java.util.stream.Stream; | |
| class Scratch { | |
| static double rnp(String pattern) { | |
| return Pattern.compile(" ").splitAsStream(pattern) | |
| .reduce(new LinkedList<>(), Scratch::accumulate, (doubles, acc) -> acc) | |
| .get(0); | |
| } | |
| static LinkedList<Double> accumulate(LinkedList<Double> acc, String next) { | |
| return switch (next) { | |
| case "+" -> Stream.concat(List.of(acc.poll() + acc.poll()).stream(), acc.stream()) | |
| .collect(Collectors.toCollection(LinkedList::new)); | |
| case "-" -> { | |
| var first = acc.poll(); | |
| var second = acc.poll(); | |
| yield Stream.concat(List.of(second - first).stream(), acc.stream()) | |
| .collect(Collectors.toCollection(LinkedList::new)); | |
| } | |
| case "*" -> Stream.concat(List.of(acc.poll() * acc.poll()).stream(), acc.stream()) | |
| .collect(Collectors.toCollection(LinkedList::new)); | |
| default -> Stream.concat(List.of(Double.parseDouble(next)).stream(), acc.stream()) | |
| .collect(Collectors.toCollection(LinkedList::new)); | |
| }; | |
| } | |
| public static void main(String[] args) { | |
| System.out.println(rnp("90 34 12 33 55 66 + * - + -")); | |
| } | |
| } |
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