03_python_deque

用python實現雙端隊列

• 採用List實現
  • List下標0作爲雙端隊列的尾端；List下標-1作爲雙端隊列的首端
  • addFront()/removeFront()函數操作複雜度爲：O(1)
  • addRear()/removeRear()函數操作複雜度爲：O(n)

class Deque:
    def __init__(self):
        self.items = []
    
    def isEmpty(self):
        return self.items == []
    
    def  addFront(self, item):
        self.items.append(item)
        
    def addRear(self, item):
        self.items.insert(0, item)
    
    def removeFront(self):
        return self.items.pop()
    
    def removeRear(self):
        return self.items.pop(0)
    
    def size(self):
        return len(self.items)
    
d = Deque()
d.addRear(4)
d.addRear('dog')
d.addFront('cat')
d.addFront(True)
print(d.size())
d.addRear(8.4)
print(d.removeRear())
print(d.removeFront())
print(d.isEmpty())

4
8.4
True
False

迴文詞判定

• 迴文詞指正讀和反讀都是一樣的詞，如radar、山東落花生花落山東
• 用雙端隊列解決迴文詞問題
  • 先將需要判定的詞從隊尾加入deque
  • 從兩端同時移除字符判定是否相同，直到deque中剩下0個或1個字符

class Deque:
    def __init__(self):
        self.items = []
    
    def isEmpty(self):
        return self.items == []
    
    def  addFront(self, item):
        self.items.append(item)
        
    def addRear(self, item):
        self.items.insert(0, item)
    
    def removeFront(self):
        return self.items.pop()
    
    def removeRear(self):
        return self.items.pop(0)
    
    def size(self):
        return len(self.items)
    
def palchecker(aString):
    chardeque = Deque()
    for ch in aString:
        chardeque.addRear(ch)
        
    stillEqual = True
    
    while chardeque.size() > 1 and stillEqual:
        first = chardeque.removeFront()
        last = chardeque.removeRear()
        if first != last:
            stillEqual = False
    return stillEqual

print(palchecker('lsdkjfskf'))
print(palchecker('radar'))

False
True