## 單向循環鏈表 單鏈表的一個變形是單向循環鏈表，鏈表中最后一個節點的next域不再為None，而是指向鏈表的頭節點。  ### 操作 * is_empty() 判斷鏈表是否為空 * length() 返回鏈表的長度 * travel() 遍歷 * add(item) 在頭部添加一個節點 * append(item) 在尾部添加一個節點 * insert(pos, item) 在指定位置pos添加節點 * remove(item) 刪除一個節點 * search(item) 查找節點是否存在 ### 實現 ~~~ class Node(object): """節點""" def __init__(self, item): self.item = item self.next = None class SinCycLinkedlist(object): """單向循環鏈表""" def __init__(self): self._head = None def is_empty(self): """判斷鏈表是否為空""" return self._head == None def length(self): """返回鏈表的長度""" # 如果鏈表為空，返回長度0 if self.is_empty(): return 0 count = 1 cur = self._head while cur.next != self._head: count += 1 cur = cur.next return count def travel(self): """遍歷鏈表""" if self.is_empty(): return cur = self._head print cur.item, while cur.next != self._head: cur = cur.next print cur.item, print "" def add(self, item): """頭部添加節點""" node = Node(item) if self.is_empty(): self._head = node node.next = self._head else: #添加的節點指向_head node.next = self._head # 移到鏈表尾部，將尾部節點的next指向node cur = self._head while cur.next != self._head: cur = cur.next cur.next = node #_head指向添加node的 self._head = node def append(self, item): """尾部添加節點""" node = Node(item) if self.is_empty(): self._head = node node.next = self._head else: # 移到鏈表尾部 cur = self._head while cur.next != self._head: cur = cur.next # 將尾節點指向node cur.next = node # 將node指向頭節點_head node.next = self._head def insert(self, pos, item): """在指定位置添加節點""" if pos <= 0: self.add(item) elif pos > (self.length()-1): self.append(item) else: node = Node(item) cur = self._head count = 0 # 移動到指定位置的前一個位置 while count < (pos-1): count += 1 cur = cur.next node.next = cur.next cur.next = node def remove(self, item): """刪除一個節點""" # 若鏈表為空，則直接返回 if self.is_empty(): return # 將cur指向頭節點 cur = self._head pre = None # 若頭節點的元素就是要查找的元素item if cur.item == item: # 如果鏈表不止一個節點 if cur.next != self._head: # 先找到尾節點，將尾節點的next指向第二個節點 while cur.next != self._head: cur = cur.next # cur指向了尾節點 cur.next = self._head.next self._head = self._head.next else: # 鏈表只有一個節點 self._head = None else: pre = self._head # 第一個節點不是要刪除的 while cur.next != self._head: # 找到了要刪除的元素 if cur.item == item: # 刪除 pre.next = cur.next return else: pre = cur cur = cur.next # cur 指向尾節點 if cur.item == item: # 尾部刪除 pre.next = cur.next def search(self, item): """查找節點是否存在""" if self.is_empty(): return False cur = self._head if cur.item == item: return True while cur.next != self._head: cur = cur.next if cur.item == item: return True return False if __name__ == "__main__": ll = SinCycLinkedlist() ll.add(1) ll.add(2) ll.append(3) ll.insert(2, 4) ll.insert(4, 5) ll.insert(0, 6) print "length:",ll.length() ll.travel() print ll.search(3) print ll.search(7) ll.remove(1) print "length:",ll.length() ll.travel() ~~~