單向迴圈連結串列

單鏈表的一個變形是單向迴圈連結串列，連結串列中最後一個節點的next域不再為None，而是指向連結串列的頭節點。

操作

• is_empty() 判斷連結串列是否為空
• length() 返回連結串列的長度
• travel() 遍歷
• add(item) 在頭部新增一個節點
• append(item) 在尾部新增一個節點
• insert(pos, item) 在指定位置pos新增節點
• remove(item) 刪除一個節點
• search(item) 查詢節點是否存在

實現

class Node(object):
    """節點"""
    def __init__(self, item):
        self.item = item
        self.next = None


class SinCycLinkedlist(object):
    """單向迴圈連結串列"""
    def __init__(self):
        self.__head = None

    def is_empty(self):
        """判斷連結串列是否為空"""
        return self.__head == None

    def length(self):
        """返回連結串列的長度"""
        # 如果連結串列為空，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):
        """遍歷連結串列"""
        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):
        """頭部新增節點"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        else:
            #新增的節點指向_head
            node.next = self.__head
            # 移到連結串列尾部，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指向新增node的
            self.__head = node

    def append(self, item):
        """尾部新增節點"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        else:
            # 移到連結串列尾部
            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):
        """在指定位置新增節點"""
        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"""
        # 若連結串列為空，則直接返回
        if self.is_empty():
            return
        # 將cur指向頭節點
        cur = self.__head
        pre = None
        while cur.next != self.__head:
            if cur.item == item:
                # 先判斷此結點是否是頭節點
                if cur == self.__head:
                    # 頭節點的情況
                    # 找尾節點
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                else:
                    # 中間節點
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        # 退出迴圈，cur指向尾節點
        if cur.item == item:
            if cur == self.__head:
                # 連結串列只有一個節點
                self.__head = None
            else:
                # pre.next = cur.next
                pre.next = self.__head

    def search(self, item):
        """查詢節點是否存在"""
        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()