AirwallexTest

package com.byron.algorithm;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.Stack;

public class AirwallexTest {
	public static void main(String[] args) {
		Stack<String> stack = new Stack<String>();
		
		@SuppressWarnings("resource")
		Scanner sc = new Scanner(System.in);
		
		List<String> operators = Arrays.asList("+", "-", "*", "/");
		
		// list for store previous data
		List<String> pre1 = new ArrayList<String>();
		List<String> pre2 = new ArrayList<String>();
		
		boolean preUndo = false;
		while (true) {
			
			String data = sc.nextLine();
			
			String[] arr = data.split(" ");
			
			
			
			// insert stack
			int errIdx = -1;
			for (int i = 0; i < arr.length; i++) {
				String d = arr[i];
				
				
				if (operators.contains(d)) {
					initPre(stack, pre1, pre2);
					
					BigDecimal s1 = getBigDecimalData(stack);
					BigDecimal s2 = getBigDecimalData(stack);
					if (null == s1 || null == s2) {
						System.out.println("operator " + d + " (position: " + i + "): insufficient parameters");
						errIdx = i;
						if (null != s2) {
							stack.push(String.valueOf(s2));
						}
						if (null != s1) {
							stack.push(String.valueOf(s1));
						}
						break;
					}
					
					if (d.equals("+")) {
						// double result = s1 + s2;
						BigDecimal result = s1.add(s2);
						stack.push(String.valueOf(result));
					} else if (d.equals("-")) {
						// double result = s2 - s1;
						BigDecimal result = s2.subtract(s1);
						stack.push(String.valueOf(result));
					} else if (d.equals("*")) {
						// double result = s2 * s1;
						BigDecimal result = s1.multiply(s2);
						stack.push(String.valueOf(result));
					} else if (d.equals("/")) {
						// double result = s2 / s1;
						BigDecimal result = s2.divide(s1);
						stack.push(String.valueOf(result));
					}
				} else if (d.equals("sqrt")) {
					BigDecimal s1 = getBigDecimalData(stack);
					if (null == s1) {
						System.out.println("operator " + d + " (position: " + i + "): insufficient parameters");
						errIdx = i;
						break;
					}
					double result = Math.sqrt(s1.doubleValue());
					if (result == (long) result) {
						stack.push(String.valueOf((long) result));
					} else {
						stack.push(String.valueOf(result));
					}
					
				} else if (d.equals("undo")) {
					if (!preUndo) {
						preUndo = true;
						// restore from pre1
						stack.clear();
						for (String pre1Data : pre1) {
							stack.add(pre1Data);
						}
					} else {
						preUndo = false;
						stack.clear();
						for (String pre2Data : pre2) {
							stack.add(pre2Data);
						}
					}
					
				} else if (d.equals("clear")) {
					stack.clear();
				} else {
					try {
						BigDecimal dd = new BigDecimal(d);
						initPre(stack, pre1, pre2);
						stack.push(d);
					} catch (Exception e) {
						break;
					}
					
				}
				
			}
			
			// read stack
			int len = stack.size();
			System.out.print("stack:");
			boolean printLn = true;
			for (int i = 0; i < len; i++) {
				
				
				printLn = false;
				if (i == len - 1) {
					System.out.println(getElement(stack, i));
				} else {
					System.out.print(getElement(stack, i) + " ");
				}
			}
			if (printLn) {
				System.out.println();
			}
			// print errs if necessary
			if (errIdx != -1) {
				String errMsg = "the ";
				boolean print = false;
				for (int i = errIdx + 1; i < arr.length; i++) {
					print = true;
					if (i == arr.length - 1) {
						errMsg += arr[(arr.length - 1)];
					} else {
						errMsg += arr[i] + ",";
					}
				}
				errMsg += " were not pushed on to the stack due to the previous error";
				if (print)
					System.out.println(errMsg);
			}
		}
		
	}
	
	static void initPre(final Stack<String> stack, List<String> pre1, List<String> pre2) {
		// store stack in pre1
		pre1.clear();
		for (String s : stack) {
			pre1.add(s);
		}
		
		if (!pre1.isEmpty()) {
			pre2.clear();
			for (int i = 0; i < pre1.size() - 1; i++) {
				pre2.add(pre1.get(i));
			}
		} 
	}
	
	static String getElement(final Stack<String> stack, int i) {
		String data = stack.elementAt(i);
		try {
			
			if (data.contains(".")) {
				BigDecimal bd = new BigDecimal(data);
				bd = bd.setScale(10, BigDecimal.ROUND_HALF_UP);
				return bd.toString();
			}
		} catch (Exception e) {
			
		}
		
		return data;
	}
	
	static BigDecimal getBigDecimalData(final Stack<String> stack) {
		try {
			String data = stack.pop();
			BigDecimal bd = new BigDecimal(data);
			return bd;
		} catch (Exception e) {
			
		}
		
		return null;
	}
	
	/*static boolean validData(String data) {
		try {
			Double.parseDouble(data);
			return true;
		} catch (Exception e) {
			
			return false;
		}
	}*/
	
}