java学习之—使用栈实现字符串数字四则运算


/**
 * 使用栈存储后缀表达式
 * Create by Administrator
 * 2018/6/13 0013
 * 下午 2:25
 **/
public class StackX {

    private int maxSize;
    private char[] stackArray;
    private int top;

    public StackX(int size)      // 构造函数
    {
        maxSize = size;
        stackArray = new char[maxSize];
        top = -1;
    }

    public void push(char j)     // 将项目放在堆栈的顶部
    {
        stackArray[++top] = j;
    }

    public char pop()            // 从堆栈顶部取项
    {
        return stackArray[top--];
    }

    public char peek()           // 从堆栈顶部查看
    {
        return stackArray[top];
    }

    public boolean isEmpty()    // 如果栈为空,则为true
    {
        return (top == -1);
    }

    public boolean isFull()     // 如果堆栈已满 true
    {
        return (top == maxSize - 1);
    }

    public int size()           // return size
    {
        return top + 1;
    }

    public char peekN(int n)     // peek at index n
    {
        return stackArray[n];
    }

    public void displayStack(String s) {
        System.out.print(s);
        System.out.print("Stack (bottom-->top): ");
        for (int j = 0; j < size(); j++) {
            System.out.print(peekN(j));
            System.out.print(' ');
        }
        System.out.println("");
    }

}

  

/**
 * 使用栈存储计算过程结果
 * Create by Administrator
 * 2018/6/14 0014
 * 上午 10:37
 **/
public class StackR {
    private int maxSize;
    private int[] stackArray;
    private int top;

    public StackR(int size)      // 构造函数
    {
        maxSize = size;
        stackArray = new int[maxSize];
        top = -1;
    }

    public void push(int j)     // 将项目放在堆栈的顶部
    {
        stackArray[++top] = j;
    }

    public int pop()            // 从堆栈顶部取项
    {
        return stackArray[top--];
    }

    public int peek()           // 从堆栈顶部查看
    {
        return stackArray[top];
    }

    public boolean isEmpty()    // 如果栈为空,则为true
    {
        return (top == -1);
    }

    public boolean isFull()     // 如果堆栈已满 true
    {
        return (top == maxSize - 1);
    }

    public int size()           // return size
    {
        return top + 1;
    }

    public int peekN(int n)     // peek at index n
    {
        return stackArray[n];
    }

    public void displayStack(String s) {
        System.out.print(s);
        System.out.print("Stack (bottom-->top): ");
        for (int j = 0; j < size(); j++) {
            System.out.print(peekN(j));
            System.out.print(' ');
        }
        System.out.println("");
    }
}

  

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * Create by Administrator
 * 2018/6/13 0013
 * 下午 2:38
 **/
public class InTOPost {

    private StackX stackX;
    private StackR stackR;
    private String input;
    private String outPut = "";

    public InTOPost(String in) {
        this.input = in;
        int stackSize = input.length();
        stackX = new StackX(stackSize);

    }

    /**
     * 中缀表达式转后缀表达式
     * @return
     */
    public String doTrans() {
        for (int i = 0; i < input.length(); i++) {
            char ch = input.charAt(i);//拿到每个字符
            stackX.displayStack("For " + ch + " ");
            switch (ch) {
                case '+':
                case '-':
                    getOpera(ch, 1);
                    break;
                case '*':
                case '/':
                    getOpera(ch, 2);
                    break;
                case ')':
                    getParen(ch);
                    break;
                case '(':
                    stackX.push(ch);
                    break;
                default:
                    outPut = outPut + ch;           //是数字将其写入输出
                    break;
            }
        }
        while (!stackX.isEmpty()) {
            stackX.displayStack("While ");
            outPut = outPut + stackX.pop();
        }
        stackX.displayStack("End ");
        return outPut;
    }

    private void getOpera(char opThis, int prec1) {
        while (!stackX.isEmpty()) {
            char opTop = stackX.pop();
            if (opTop == '(') {
                stackX.push(opTop);
                break;
            } else {
                int prec2;
                if (opTop == '+' || opTop == '-') {
                    prec2 = 1;
                } else {
                    prec2 = 2;
                }
                if (prec2 < prec1) {
                    stackX.push(opTop);
                    break;
                } else {
                    outPut = outPut + opTop;
                }
            }
        }
        stackX.push(opThis);
    }

    private void getParen(char ch) {
        while (!stackX.isEmpty()) {
            char chx = stackX.pop();
            if (chx == '(') {
                break;
            } else {
                outPut = outPut + chx;
            }
        }
    }

    /**
     * 计算后缀表达式的结果
     * @param output
     * @return
     */
    public int doParse(String output) {
        stackR = new StackR(20);            //新建堆栈
        char ch;
        int num1, num2, interAns;
        for (int i = 0; i < output.length(); i++) { //遍历后缀表达式的字符串
            ch = output.charAt(i);               // 读取到每一个字符
            stackR.displayStack(ch + " ");
            if (ch >= '0' && ch <= '9') {        // 判断是不是数字
                stackR.push((int) (ch - '0'));   // 放入到栈里
            } else {
                num2 = stackR.pop();             // 如果不是数字,就从栈里取出两个数字
                num1 = stackR.pop();
                switch (ch) {                   // 判断是哪个运算符,并计算
                    case '+':
                        interAns = num1 + num2;
                        break;
                    case '-':
                        interAns = num1 - num2;
                        break;
                    case '*':
                        interAns = num1 * num2;
                        break;
                    case '/':
                        interAns = num1 / num2;
                        break;
                    default:
                        interAns = 0;
                }
                stackR.push(interAns);      // 把计算结果放入栈里
            }
        }
        interAns = stackR.pop();           // 获得最终结果
        return interAns;
    }

    /**
     * 获取用户输入
     * @return
     * @throws IOException
     */
    public static String getString() throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        String s = br.readLine();
        return s;
    }

    public static void main(String[] args) throws IOException {
        String input, output;
        while (true) {
            System.out.print("Enter infix: ");
            System.out.flush();
            input = getString();
            if (input.equals("")) {
                break;
            }
            InTOPost toPost = new InTOPost(input);
            output = toPost.doTrans();
            System.out.println("Postfix is " + output + "\n");
            int result = toPost.doParse(output);
            System.out.println("结果:" + result);
        }
    }

  运行测试:

请输入:  (4+2*3)/2

For ( Stack (bottom-->top):
For 4 Stack (bottom-->top): (
For + Stack (bottom-->top): (
For 2 Stack (bottom-->top): ( +
For * Stack (bottom-->top): ( +
For 3 Stack (bottom-->top): ( + *
For ) Stack (bottom-->top): ( + *
For / Stack (bottom-->top):
For 2 Stack (bottom-->top): /
While Stack (bottom-->top): /
End Stack (bottom-->top):
Postfix is 423*+2/

4 Stack (bottom-->top):
2 Stack (bottom-->top): 4
3 Stack (bottom-->top): 4 2
* Stack (bottom-->top): 4 2 3
+ Stack (bottom-->top): 4 6
2 Stack (bottom-->top): 10
/ Stack (bottom-->top): 10 2
结果:5


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