Codewars #14 Calculator (3kyu)

#14 Calculator

Create a simple calculator that given a string of operators (+ - * and /) and numbers separated by spaces returns the value of that expression

Example:

Calculator.evaluate("2 / 2 + 3 * 4 - 6") // => 7

Remember about the order of operations! Multiplications and divisions have a higher priority and should be performed left-to-right. Additions and subtractions have a lower priority and should also be performed left-to-right.

면접볼때는 달달 외워다녔던것 같은데 오랜만에하니까 영..깔끔하지도 않고

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Stack;
import java.util.StringTokenizer;

public class Calculator {
	public static Double evaluate(String expression) {
		// your code here

		Map<String,Integer> weight = new HashMap<String,Integer>();
		weight.put("+", 1);
		weight.put("-", 1);
		weight.put("*", 2);
		weight.put("/", 2);
		
		List<String> postfix = new ArrayList<String>(); 
		StringTokenizer tokenizer = new StringTokenizer(expression," ");
		Stack<String> stack = new Stack<String>();
		
		while (tokenizer.hasMoreElements()) {
			String token =tokenizer.nextToken();
			if(token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/")) {
					while(!stack.isEmpty() && weight.get(token) <= weight.get(stack.peek())) {
						postfix.add(stack.pop());
					}
					stack.push(token);
			}else {
				postfix.add(token);
			}
		}
		
		while(!stack.isEmpty()) {
			postfix.add(stack.pop());
		}
		
		for (String str : postfix) {
			if(str.equals("+") || str.equals("-") || str.equals("*") || str.equals("/")) {
				if(str.equals("+")) {
					stack.push(String.valueOf(Double.parseDouble(stack.pop())+Double.parseDouble(stack.pop())));
				}else if(str.equals("-")){
					double temp = Double.parseDouble(stack.pop());
					stack.push(String.valueOf(Double.parseDouble(stack.pop())-temp));
				}else if(str.equals("*")){
					stack.push(String.valueOf(Double.parseDouble(stack.pop())*Double.parseDouble(stack.pop())));
				}else {
					double temp = Double.parseDouble(stack.pop());
					stack.push(String.valueOf(Double.parseDouble(stack.pop())/temp));
				}
			}else {
				stack.push(str);
			}
		}

		return Double.parseDouble(stack.pop());
	}
}