栈实现计算器

思路：
1.使用数组模拟栈
2. 创建数据栈和运算符栈，遍历字符串
3. 判断该字符是运算符还是数据，如果是数据则入栈，如果是运算符则判断该运算符的与栈中运算符的优先级；如果栈中运算符优先级大，则数据栈pop两个数据进行运算
然后将结果入数据栈，遍历的运算符入运算符栈；如果是遍历的运算符优先级较大，则将该运算符入栈

package com.company;

/**
 * @author:抱着鱼睡觉的喵喵
 * @date:2021/2/18
 * @description:
 */

public class Calculator {
    /**
     * 使用栈实现计算器的思路:
     * 1.创建数据栈和运算符栈，遍历字符串
     * 2.判断该字符是运算符还是数据，如果是数据则入栈，如果是运算符则判断该运算符的与栈中运算符的优先级；如果栈中运算符优先级大，则数据栈pop两个数据进行运算
     * 然后将结果入数据栈，遍历的运算符入运算符栈；如果是遍历的运算符优先级较大，则将该运算符入栈
     *
     * @param args
     */
    public static void main(String[] args) {
        ArrayStack2 numStack = new ArrayStack2(10);
        ArrayStack2 opStack = new ArrayStack2(10);
        int index = 0;
        int num1 = 0;
        int num2 = 0;
        int op = 0;
        int result = 0;
        String s = "30*2-1+50";
        char ch = ' ';
        String temp = "";
        while (true) {
            ch = s.substring(index, index + 1).charAt(0);
            if (opStack.isOp(ch)) {
                if (!opStack.isEmpty()) {
                    if (opStack.priority(ch) <= opStack.priority(opStack.peek())) {
                        num1 = numStack.pop();
                        num2 = numStack.pop();
                        op = opStack.pop();
                        result = numStack.cal(num1, num2, op);
                        numStack.push(result);
                        opStack.push(ch);
                    } else {
                        opStack.push(ch);
                    }
                } else {
                    opStack.push(ch);
                }
            } else {
                //需要考虑多位数的情况

                temp += ch;
                if (index == s.length() - 1) {
                    numStack.push(Integer.parseInt(temp));
                }else {
                    if (opStack.isOp(s.substring(index+1,index+2).charAt(0))) {
                        numStack.push(Integer.parseInt(temp));
                        temp = "";
                    }
                }

            }
            index++;
            if (index >= s.length()) {
                break;
            }
        }
        while (true) {
            if (opStack.isEmpty()) {
                break;
            }
            num1 = numStack.pop();
            num2 = numStack.pop();
            op = opStack.pop();
            result = numStack.cal(num1, num2, op);
            numStack.push(result);
        }
        int res2 = numStack.pop();
        System.out.println(res2);
    }
}

class ArrayStack2 {
    private int maxSize;
    private int[] stack;
    private int top = -1;

    public ArrayStack2(int maxSize) {
        this.maxSize = maxSize;
        stack = new int[maxSize];
    }

    public boolean isFull() {
        return top == maxSize - 1;
    }

    public boolean isEmpty() {
        return top == -1;
    }

    //返回栈顶数据
    public int peek() {
        return stack[top];
    }

    //入栈
    public void push(int value) {
        if (isFull()) {
            System.out.println("栈已满！");
            return;
        }
        top++;
        stack[top] = value;
    }

    //出栈
    public int pop() {
        if (isFull()) {
            System.out.println("栈空！");
            throw new RuntimeException("栈空");
        }
        int result = stack[top];
        top--;
        return result;
    }

    //返回运算符的优先级
    public int priority(int op) {
        if (op == '*' || op == '/') {
            return 1;
        } else if (op == '+' || op == '-') {
            return 0;
        } else {
            return -1;
        }
    }

    public boolean isOp(char s) {
        return s == '+' || s == '-' || s == '*' || s == '/';
    }

    /**
     * 计算
     *
     * @param num1 出栈的第一个数据
     * @param num2 出栈的第二个数据
     * @param op   出栈的运算符
     * @return
     */
    public int cal(int num1, int num2, int op) {
        int result = 0;
        switch (op) {
            case '+':
                result = num2 + num1;
                break;
            case '-':
                result = num2 - num1;
                break;
            case '*':
                result = num2 * num1;
                break;
            case '/':
                result = num2 / num1;
                break;
            default:
                break;
        }
        return result;
    }
}