順序棧

三個基本屬性

• 棧的儲存資料data

• 棧的最大儲存量maxSize

• 棧頂top

Python實現

# Python 2.7

class sqStack(object):

    # 初始化
    def __init__(self, maxSize):
        self.data = [None] * maxSize
        self.maxSize = maxSize
        self.top = -1

    # 獲取順序棧長度  
    def get_length(self):
        return
 
 self.top + 1

    # 清空順序棧   
    def clear(self):
        for i in range(self.get_length()):
            self.data[i] = None
        self.top = -1

    # 是否為空
    def is_empty(self):
        return self.top == -1

    # 是否滿
    def is_full(self):
        return self.get_length() == self.maxSize

    # 進棧
 

    def push(self, elem):
        if self.is_full():
            print 'Stack is full!'
        else:
            self.top += 1
            self.data[self.top] = elem

    # 出棧
    def pop(self):
        if self.is_empty():
            print 'Stack is empty!'
        else:
            self.top -= 1
 

            return self.data[self.top + 1]

    # 取棧頂元素
    def get_top(self):
        if self.is_empty():
            print 'Stack is empty!'
        else:
            return self.data[self.top]

    # 由棧頂列印棧元素
    def show_stack(self):
        for i in range(self.get_length()-1, -1, -1):
            print self.data[i]

鏈式棧

節點的基本屬性

• 資料域data

• 後繼指標next

鏈式棧的基本屬性

• 棧頂

• 鏈式棧的長度

Python實現

# Python 2.7

# 節點
class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

# 連結串列
class lkStack(object):

    # 初始化
    def __init__(self):
        self.top = Node(None)
        self.length = 0

    # 是否為空
    def is_empty(self):
        return self.length == 0

    # 獲取連結串列長度
    def get_length(self):
        return self.length

    # 進棧
    def push(self, elem):
        node = Node(elem, self.top)
        self.top = node
        self.length += 1

    # 出棧
    def pop(self):
        if self.length == 0:
            print 'lkStack is empty!'
        else:
            top = self.top
            self.top = self.top.next
            self.length -= 1
            return top.data

    # 展示連結串列
    def show(self):
        if self.is_empty():
            print 'lkList is empty!'
        else:
            p = self.top
            for i in range(self.length):
                print p.data
                p = p.next

棧的應用–四則運算表示式求值

字尾（逆波蘭）表示法

• 中綴表示法：9+(3-1)*3+10/2

• 字尾表示法：9 3 1 - 3 * + 10 2 / +

中綴轉字尾

# Python 2.7

# 將中綴字串轉換成陣列
def str2list(calc_str):
# calc_str = '9+(3-1)*3+10/2'
    symbol_list = ['+', '-', '*', '/', '(', ')']
    calc_list = [calc_str]
    for symbol in symbol_list:
        str_list = []
        for part in calc_list:
            part_list = part.split(symbol)
            temp = []
            for item in part_list:
                if item:  # 非空時追加
                    temp.append(item)
                temp.append(symbol)
            del temp[-1]
            if temp:  # 非空時追加
                str_list.extend(temp)
        calc_list = str_list
    return calc_list

# 中綴轉字尾
def mid_after(calc_str):    
    mid2after = lkStack()
    mid_list = str2list(calc_str)
    after_list = []
    symbol_list = ['+', '-', '*', '/', '(', ')']
    symbol_value = {'(':-2, None:-1, '+':0, '-':0, '*':1, '/':1}
    for item in mid_list:
        if item not in symbol_list:
            after_list.append(item)
        else:
            if item == ')':
                while mid2after.top.data != '(': 
                    top = mid2after.pop()
                    after_list.append(top)
                top = mid2after.pop()
            else:
                if item == '(':
                    mid2after.push(item)
                else:
                    if symbol_value[item] > symbol_value[mid2after.top.data]:
                        mid2after.push(item)
                    if symbol_value[item] < symbol_value[mid2after.top.data]:
                        while symbol_value[item] <= symbol_value[mid2after.top.data]:
                            top = mid2after.pop()
                            after_list.append(top)
                        mid2after.push(item)
    while not mid2after.is_empty():
        top = mid2after.pop()
        after_list.append(top)
    return after_list

通過後綴表示式求值

# Python 2.7

def after_calc(after_list):
    symbol_list = ['+', '-', '*', '/']
    stack = lkStack()
    for item in after_list:
        if item not in symbol_list:
            stack.push(item)
        else:
            var1 = float(stack.pop())
            var2 = float(stack.pop())
            if item == '+':
                result = var2 + var1
            elif item == '-':
                result = var2 - var1
            elif item == '*':
                result = var2 * var1
            else:
                result = var2 / var1
            stack.push(str(result))
    return float(stack.top.data)

測試

# Python 2.7

calc_str = '12+((12-7)*(11-2)-6)*12'
calc_list = str2list(calc_str)
after_list = mid_after(calc_str)
result = after_calc(after_list)

廣告時間

個人部落格：http://ruanshubin.top
GitHub：https://github.com/Ruanshubin/

歡迎您掃一掃上面的二維碼，關注我的微信公眾號！