python数据结构与算法分析（第二版）算法题（1）

自留用来复习期末考的！如有错误也欢迎批评指正！

首先复习栈和队列的相关算法题，都不算太难。

1.利用两个栈实现回文检测器：不限制回文的大小写，不限制回文中添加空格。（下面这个办法是最简单的，也是最好理解的）

from pythonds.basic import Stack
def palchecker(astring):
    s1=Stack()
    s2=Stack()
    astring=astring.lower()
    astring=astring.replace(' ','')
    for j in astring:
        s1.push(j)
    for j in astring:
        s2.push(s1.pop())
    for j in astring:
        s1.push(j)
    for i in range(len(astring)):
        if s1.pop()!=s2.pop():
            return False
    return True  #注意return的位置要在循环结束之后

2.利用一个栈和一个队列实现回文检测器，回文输入的要求同题1。

from pythonds.basic import Stack, Queue

def palchecker(aString):
    aString = aString.lower()
    aString = aString.replace(' ', '')
    s = Stack()
    q = Queue()
    length = len(aString)
    mid = length // 2
    for ch in aString:
        q.enqueue(ch)
    for i in range(mid):
        s.push(q.dequeue())
    if length % 2 == 1:
        q.dequeue()
    for j in range(mid):  
        if s.pop() != q.dequeue():
            return False
return True

3.用栈来检查式子中的括号是否匹配

from pythonds.basic import Stack
def parChecker(symbolString):
    s = Stack()
    balanced = True
    index = 0  #存游标
    match = True
    while index < len(symbolString) and balanced:
        symbol = symbolString[index]  #存游标对应的值
        if symbol in "([{":
            s.push(symbol)
        elif symbol in ")]}":
            if s.isEmpty():
                balanced = False
            else:
                top = s.pop()
                if top=='(' and symbol == ')'