python實現二叉樹的構建和遍歷

# coding=utf-8


class Node(object): def __init__(self, data=None, left_child=None, right_child=None): self.data = data self.left_child = left_child self.right_child = right_child class BTree(object): def __init__(self): self.root = None def add_node(self, data): node = Node(data) if self.root is None: self.root = node return tmp_queue = [self.root] while True: current_node = tmp_queue.pop(0) if current_node is None: return
            if current_node.left_child is None: current_node.left_child = node return
            elif current_node.right_child is None: current_node.right_child = node return tmp_queue.append(current_node.left_child) tmp_queue.append(current_node.right_child) def front_travel(self, node): """先序遍歷"""
        if node is None: return
        print(node.data) self.front_travel(node.left_child) self.front_travel(node.right_child) def middle_travel(self, node): """中序遍歷"""
        if node is None: return self.middle_travel(node.left_child) print(node.data) self.middle_travel(node.right_child) def last_travel(self, node): """後序遍歷"""
        if node is None: return self.last_travel(node.left_child) self.last_travel(node.right_child) print(node.data) def level_travel(self): """層次遍歷""" tmp_queue = [self.root] while True: if len(tmp_queue) == 0: print("travel finish") return current_node = tmp_queue.pop(0) print(current_node.data) if current_node.left_child: tmp_queue.append(current_node.left_child) if current_node.right_child: tmp_queue.append(current_node.right_child) def front(self): """堆棧前序遍歷"""
        if not self.root: return tmp_stack = [] node = self.root while tmp_stack or node: while node: print(node.data) tmp_stack.append(node) node = node.left_child node = tmp_stack.pop() node = node.right_child def middle(self): """堆棧中序遍歷"""
        if not self.root: return tmp_stack = [] node = self.root while tmp_stack or node: while node: tmp_stack.append(node) node = node.left_child node = tmp_stack.pop() print(node.data) node = node.right_child def last(self): """堆棧後序遍歷，較難"""
        if not self.root: return tmp_node = self.root tmp_stack = [] while tmp_node or tmp_stack: while tmp_node: tmp_stack.append(tmp_node) tmp_node = tmp_node.left_child or tmp_node.right_child tmp_node = tmp_stack.pop() print(tmp_node.data) if tmp_stack and tmp_stack[-1].left_child is tmp_node: tmp_node = tmp_stack[-1].right_child else: tmp_node = None if __name__ == "__main__": tree = BTree() for i in range(1, 20): tree.add_node(i) # tree.level_travel() # 廣度遍歷
    # tree.front_travel(tree.root) # 遞歸前序遍歷
    # tree.middle_travel(tree.root) # 遞歸中序遍歷
    tree.last_travel(tree.root)  # 遞歸後序遍歷
    print("---" * 20) # tree.front() # 堆棧前序遍歷
    # tree.middle() # 堆棧中序遍歷
    tree.last()  # 堆棧後序遍歷

 

 總結：

　　總結了一下二叉樹的構建和遍歷，參考了一下網上其餘的博客，有些博客寫的很好，可是更多博客的算法要麼囉裏囉嗦，要麼代碼質量不高，讀起來很費力，因此本身從新寫了一遍。其中堆棧後序遍歷稍微麻煩一些，有點難理解，建議在紙上畫一下圖。