Main.java

RPN計算機(状態出力付き)

package org.zakky.rpn;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Stack;
import java.util.concurrent.TimeUnit;

public class Main {

    public static void main(String[] args) throws Exception {
        final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String line = reader.readLine();
        final Stack<Long> s = new Stack<Long>();
        final String[] inputs = line.split(" +");
        printStack(s);
        for (String input : inputs) {
            System.out.println("input is " + input);
            if (Character.isDigit(input.charAt(0))) {
                s.push(Long.valueOf(input));
                System.out.println("pushed " + input);
            } else if (input.charAt(0) == '+') {
                final long v2 = s.pop();
                System.out.println("poped " + v2);
                final long v1 = s.pop();
                System.out.println("poped " + v1);
                s.push(v1 + v2);
                System.out.println("pushed " + v1 + " + " + v2);
            } else if (input.charAt(0) == '-') {
                final long v2 = s.pop();
                System.out.println("poped " + v2);
                final long v1 = s.pop();
                System.out.println("poped " + v1);
                s.push(v1 - v2);
                System.out.println("pushed " + v1 + " - " + v2);
            } else if (input.charAt(0) == '*') {
                final long v2 = s.pop();
                System.out.println("poped " + v2);
                final long v1 = s.pop();
                System.out.println("poped " + v1);
                s.push(v1 * v2);
                System.out.println("pushed " + v1 + " * " + v2);
            } else if (input.charAt(0) == '/') {
                final long v2 = s.pop();
                System.out.println("poped " + v2);
                final long v1 = s.pop();
                System.out.println("poped " + v1);
                s.push(v1 / v2);
                System.out.println("pushed " + v1 + " / " + v2);
            }
            printStack(s);
        }
        System.out.println((s.size() == 1) ? ("The answer is " + s.pop())
                : ("invalid RPN expression: " + line));
    }

    private static void printStack(Stack<?> s) {
        final StringBuilder sb = new StringBuilder("stack = [");
        for (int i = s.size() - 1; 0 <= i; i--) {
            sb.append(s.get(i));
            sb.append(",");
        }
        if (!s.isEmpty()) {
            sb.setLength(sb.length() - ",".length());
        }
        sb.append("]");
        System.out.println(sb.toString());
    }
}