golang数据结构之利用栈求计算表达式（加减乘除）

例如：3+2*6-2

先定义两个栈，一个为数值栈，一个为运算符栈；

stack.go

package stack

import (
    "errors"
    "fmt"
)

type Stack struct {
    MaxTop int     //栈最大可以存放的数量
    Top    int     //栈顶
    Arr    [20]int //模拟栈
}

func (s *Stack) Push(val int) (err error) {
    //先判断栈是否满了
    if s.Top == s.MaxTop-1 {
        fmt.Println("栈满了")
        return errors.New("栈满了")
    }
    s.Top++
    s.Arr[s.Top] = val
    return
}

func (s *Stack) Pop() (val int, err error) {
    if s.Top == -1 {
        fmt.Println("栈已空")
        return -1, errors.New("栈已空")
    }
    val = s.Arr[s.Top]
    s.Arr[s.Top] = 0
    s.Top--
    return val, nil

}

func (s *Stack) Show() {
    if s.Top == -1 {
        fmt.Println("栈为空")
        return
    }
    tmp := s
    for i := tmp.Top; i >= 0; i-- {
        fmt.Printf("Arr[%d]=%v
", i, tmp.Arr[i])
    }
    return
}

//判断一个字符是数字还是加减乘除
func (s *Stack) IsOper(val int) bool {
    if val == 42 || val == 43 || val == 45 || val == 47 {
        return true
    } else {
        return false
    }
}

//运算的方法
func (s *Stack) Cal(num1 int, num2 int, oper int) int {
    res := 0
    switch oper {
    //乘法
    case 42:
        res = num2 * num1
    //加法
    case 43:
        res = num2 + num1
    //减法
    case 45:
        res = num2 - num1
    //除法
    case 47:
        res = num2 / num1
    default:
        fmt.Println("运算符错误")
    }
    return res
}

//定义优先级
func (s *Stack) Priority(oper int) int {
    res := 0
    if oper == 42 || oper == 47 {
        res = 1
    } else if oper == 43 || oper == 45 {
        res = 0
    }
    return res
}

main.go

package main

import (
    "fmt"
    "go_code/data_structure/stack"
    "strconv"
)

func main() {

    str := "30+2*6-600/2"
    n := len(str)
    numStack := &stack.Stack{
        MaxTop: n,
        Top:    -1,
    }
    operStack := &stack.Stack{
        MaxTop: n,
        Top:    -1,
    }
    index := 0
    num1 := 0
    num2 := 0
    oper := 0
    result := 0
    keepNum := ""
    for {
        ch := str[index : index+1]
        //字符对应的ASCII码值
        tmp := int([]byte(ch)[0])
        if operStack.IsOper(tmp) {
            if operStack.Top == -1 {
                operStack.Push(tmp)
            } else {
                //判断栈顶的优先级
                if operStack.Priority(operStack.Arr[operStack.Top]) >=
                    operStack.Priority(tmp) {
                    num1, _ = numStack.Pop()
                    num2, _ = numStack.Pop()
                    oper, _ = operStack.Pop()
                    result = operStack.Cal(num1, num2, oper)
                    //将计算的结果重新入栈
                    numStack.Push(result)
                    //当前符号重新入栈
                    operStack.Push(tmp)
                } else {
                    operStack.Push(tmp)
                }
            }

        } else {
            //判断型如30等数字
            keepNum += ch

            if index == n-1 {
                val, _ := strconv.ParseInt(keepNum, 10, 64)
                numStack.Push(int(val))
            } else {
                //向index后面探以位
                if operStack.IsOper(int([]byte(str[index+1 : index+2])[0])) {
                    val, _ := strconv.ParseInt(keepNum, 10, 64)
                    numStack.Push(int(val))
                    keepNum = ""
                }
            }
            //入栈的数要是int型
            // val, _ := strconv.ParseInt(ch, 10, 64)
            // numStack.Push(int(val))
        }
        if index == n-1 {
            break
        }
        //继续扫描
        index++
    }

    //如果表达式扫描完毕，依次取出符号和两位数进行运算
    for {
        if operStack.Top == -1 {
            break
        }
        num1, _ = numStack.Pop()
        num2, _ = numStack.Pop()
        oper, _ = operStack.Pop()
        result = operStack.Cal(num1, num2, oper)
        //将计算的结果重新入栈
        numStack.Push(result)
    }

    res, _ := numStack.Pop()
    fmt.Printf("计算表达式 %v 的值是：%v
", str, res)
}

运行结果：