能否用Java的Stack類(lèi)實(shí)現(xiàn)表達(dá)式求值

小樊
81
2024-09-23 21:50:41

是的，你可以使用Java的Stack類(lèi)來(lái)實(shí)現(xiàn)表達(dá)式求值。這里是一個(gè)簡(jiǎn)單的例子，展示了如何使用Stack類(lèi)實(shí)現(xiàn)中綴表達(dá)式到后綴表達(dá)式（逆波蘭表示法）的轉(zhuǎn)換以及計(jì)算后綴表達(dá)式的值：

import java.util.Stack;
import java.util.StringTokenizer;

public class ExpressionEvaluator {
    public static void main(String[] args) {
        String expression = "3 + 4 * 2 / ( 1 - 5 ) ^ 2";
        String postfix = convertToPostfix(expression);
        int result = evaluatePostfix(postfix);
        System.out.println("Result: " + result);
    }

    public static String convertToPostfix(String expression) {
        Stack<String> stack = new Stack<>();
        StringTokenizer tokenizer = new StringTokenizer(expression);

        while (tokenizer.hasMoreTokens()) {
            String token = tokenizer.nextToken();

            if (isOperator(token)) {
                String topOperand = stack.pop();
                String secondOperand = stack.pop();
                String result = performOperation(topOperand, secondOperand, token);
                stack.push(result);
            } else {
                stack.push(token);
            }
        }

        return stack.pop();
    }

    public static int evaluatePostfix(String postfix) {
        Stack<Integer> stack = new Stack<>();

        for (String token : postfix.split(" ")) {
            int operand = Integer.parseInt(token);
            stack.push(operand);
        }

        return stack.pop();
    }

    public static boolean isOperator(String token) {
        return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/") || token.equals("^");
    }

    public static String performOperation(String operand1, String operand2, String operator) {
        int num1 = Integer.parseInt(operand1);
        int num2 = Integer.parseInt(operand2);

        switch (operator) {
            case "+":
                return String.valueOf(num1 + num2);
            case "-":
                return String.valueOf(num1 - num2);
            case "*":
                return String.valueOf(num1 * num2);
            case "/":
                return String.valueOf(num1 / num2);
            case "^":
                return String.valueOf(Math.pow(num1, num2));
            default:
                throw new IllegalArgumentException("Invalid operator: " + operator);
        }
    }
}

這個(gè)例子中，我們首先將中綴表達(dá)式轉(zhuǎn)換為后綴表達(dá)式，然后計(jì)算后綴表達(dá)式的值。注意，這個(gè)例子僅支持整數(shù)運(yùn)算，如果你需要支持浮點(diǎn)數(shù)運(yùn)算，可以將Integer.parseInt()替換為Double.parseDouble()，并在計(jì)算時(shí)進(jìn)行相應(yīng)的類(lèi)型轉(zhuǎn)換。

0 踩