用python实现简单的调度场算法

Posted 2020-08-21

#因本人水平有限，目前只是简单实现了调度场算法，只支持+,-,*,/,%操作。其他待补充

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

from sys import argv
from decimal import *

def delBlank(str):
    """
    Delete all blanks in the str
    """
    ans = ""
    for e in str:
        if e != " ":
            ans += e
    return  ans
def getPriority(c):
    """
    操作符中："+、-优先级低，*、/、%优先级高" ,^待续
    """
    if (c==‘+‘ or c==‘-‘):
        return 0
    elif(c == ‘*‘ or c == ‘/‘ or c == ‘%‘):
        return  1
    elif (c==‘^‘):
        return 2


def infix2postfix(str):
    """
    把中值表达式转化为后值表达式。
    """
    postfix = []
    stackOfOperator = []
    index,pos,length = -1,0,len(str)
    while(index < length-1):#python for index in range(length):不行，不馆循环内是否更改index，index都是会从1到length-1。
        index +=1
        char = str[index]
        if(char in "0123456789"):#如果是数字，直接输出
            pos = index
            while(index <length and str[index] in "0123456789"):
                index +=1
            postfix.append(str[pos:index])
            index -= 1
            continue
        elif(char == ‘)‘):#)右括号，将栈中元素弹出只至左括号，且左括号和右括号不加入到后缀表达式
            while(True):
                tmp = stackOfOperator.pop()
                if(tmp=="("):
                    break
                postfix.append(tmp)
        elif(char == "("):#左括号直接压入栈中
            stackOfOperator.append(char)
        else:
            if len(stackOfOperator) == 0:#如果栈为空，则直接压入
                stackOfOperator.append(char)
                continue
            top = stackOfOperator[-1]
            if (top == ‘(‘):#操作符栈顶为左括号(，则将当前操作符入栈。
                stackOfOperator.append(char)
                continue
            if(getPriority(char)<=getPriority(top)):
            #如果此操作符(+,-,*,/,%)的优先级小于或等于栈顶的元素
            #则将栈中元素弹出至(1)遇到左括号(2)栈顶元素为更低优先级(3)栈为空为止
            #并将弹出的元素加入后缀表达式中，将单曲操作数压入栈中
                while(True):
                    tmp = stackOfOperator[-1]
                    if(tmp == ‘(‘ or tmp == getPriority(tmp) < getPriority(char)):
                        break
                    postfix.append(tmp)
                    stackOfOperator.pop()
                    if len(stackOfOperator)==0:
                        break
                stackOfOperator.append(char)
            else:
            #如果当前操作符优先级大于此时当前栈顶操作数，则讲当前操作数压入栈
                stackOfOperator.append(char)
    while(len(stackOfOperator)):
        postfix.append(stackOfOperator.pop())
    return postfix

def operate(num1,num2,operator):
    if operator == "+":
        return num1 + num2
    elif operator == "-":
        return num1 - num2
    elif operator == "*":
        return  num1 * num2
    elif operator == "/":
        return num1 / num2
    elif operator == "%":
        return num1 % num2
    elif operator == "^":
        return num1 ** num2
‘‘‘
通过后缀表达式计算数值
1、从左到有遍历表达式的每个数字和符号，若是遇到数字则进栈，遇到运算符则将栈顶两个元素出栈，进行运算并将运算结果进栈
2、遍历完后缀表达式，此时栈中剩余的数字就是运算结果
‘‘‘
def calculateByPostfix(postifix):
    stackOfNumber =[]
    index,length = 0,len(postifix)
    while index < length:
        e = postifix[index]
        if e in "+-*/%":#后进先出
            num2 = float(stackOfNumber.pop())
            num1 = float(stackOfNumber.pop())
            stackOfNumber.append(operate(num1,num2,e))
            print(stackOfNumber)
        else:
            stackOfNumber.append(e)
            print(stackOfNumber)
        index += 1
    return stackOfNumber
if __name__ == ‘__main__‘:
#get the exp
    exp = ""
    for i in range(len(argv)-1):
        exp += argv[i+1]
    exp = delBlank(exp)
    postfix=infix2postfix(exp)
    print(postfix)
    print(calculateByPostfix(postfix))