Python 单链表实现&基础函数

class LNode:
    def __init__(self, elem, next_ = None):
        self.elem = elem
        self.next = next_

class LList:
    def __init__(self):
        self._head = None

    def is_empty(self):
        return self._head is None

    # 前端插入
    def prepend(self, elem):
        self._head = LNode(elem, self._head)

    # 删除头结点并返回
    def pop_first(self):
        if self.is_empty():
            raise LinkedListUnderFlow("in pop")
        e = self._head.elem
        self._head = self._head.next
        return e

    def append(self, elem):
        if self.is_empty():
            self._head = LNode(elem)
            return
        p = self._head
        while p.next:
            p = p.next
        p.next = LNode(elem)

    def pop(self):
        if self.is_empty():
            raise LinkedListUnderFlow("in pop")
        p = self._head
        if p.next is None:
            e = p.elem
            self._head = None
            return e

        # 用p.next.next做条件是因为把最后一个结点删除，需要找到倒数第二个结点
        while p.next.next is not None:
            p = p.next
        e = p.next.elem
        p.next = None
        return e

    def find(self, pred):
        p = self._head
        while p.next is not None:
            if pred(p.elem):
                # 构建生成器，找到了一个元素可以继续找下一个
                yield p.elem
            p = p.next


    def printall(self):
        p = self._head
        while p is not None:
            print(p.elem, end="")
            if p.next is not None:
                print(", ", end="")
            p = p.next

        # 换行，因为默认end参数为 "\n"
        # 等价 print("\n", end="")
        print("")

if __name__ == '__main__':
    my_list = LList()
    for i in range(10, 0, -1):
        my_list.prepend(i)
    my_list.printall()    # 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
    for i in range(11, 21):
        my_list.append(i)
    my_list.printall()
    print(my_list.pop())  # 20
    print(my_list.pop_first()) # 1
    my_list.printall()   # 2~19

    def find_odd(n):
        if n % 2 != 0:
            return n
    for i in my_list.find(find_odd):
        print(i)         # 1, 3, 5, 7, 9 ,...