Python实现栈

栈的操作

• Stack() 创建一个新的空栈
• push(item) 添加一个新的元素item到栈顶
• pop() 弹出栈顶元素
• peek() 返回栈顶元素
• is_empty() 判断栈是否为空
• size() 返回栈的元素个数

class Stack:
     def __init__(self):
         self.items = []

     def isEmpty(self):
         return self.items == []

     def push(self, item):
         self.items.append(item)

     def pop(self):
         return self.items.pop()

     def peek(self):
         return self.items[len(self.items)-1]

     def size(self):
         return len(self.items)

from pythonds.basic.stack import Stack

s = Stack()

print(s.isEmpty())
s.push(4)
s.push('dog')
print(s.peek())
s.push(True)
print(s.size())
print(s.isEmpty())
s.push(8.4)
print(s.pop())
print(s.pop())
print(s.size())

 用栈处理简单括号匹配问题

from pythonds.basic.stack import Stack

def parChecker(symbolString):
    s = Stack()
    balanced = True
    index = 0
    while index < len(symbolString) and balanced:
        symbol = symbolString[index]
        if symbol == "(":
            s.push(symbol)
        else:
            if s.isEmpty():
                balanced = False
            else:
                s.pop()

        index = index + 1

    if balanced and s.isEmpty():
        return True
    else:
        return False

print(parChecker('((()))'))
print(parChecker('(()'))

多括号匹配问题

from pythonds.basic.stack import Stack

def parChecker(symbolString):
    s = Stack()
    balanced = True
    index = 0
    while index < len(symbolString) and balanced:
        symbol = symbolString[index]
        if symbol in "([{":
            s.push(symbol)
        else:
            if s.isEmpty():
                balanced = False
            else:
                top = s.pop()
                if not matches(top,symbol):
                       balanced = False
        index = index + 1
    if balanced and s.isEmpty():
        return True
    else:
        return False

def matches(open,close):
    opens = "([{"
    closers = ")]}"
    return opens.index(open) == closers.index(close)


print(parChecker('{{([][])}()}'))
print(parChecker('[{()]'))

 进制转换

from pythonds.basic.stack import Stack

def baseConverter(decNumber,base):
    digits = "0123456789ABCDEF"

    remstack = Stack()

    while decNumber > 0:
        rem = decNumber % base
        remstack.push(rem)
        decNumber = decNumber // base

    newString = ""
    while not remstack.isEmpty():
        newString = newString + digits[remstack.pop()]

    return newString

print(baseConverter(25,2))
print(baseConverter(25,16))