# 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): """先序遍历""" 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): """中序遍历""" 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): """后序遍历""" if node is None: return self.last_travel(node.left_child) self.last_travel(node.right_child) print(node.data) def level_travel(self): """层次遍历""" 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): """堆栈前序遍历""" 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): """堆栈中序遍历""" 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): """堆栈后序遍历，较难""" 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 () # breadth traversal # Tree.front_travel (tree.root) before the recursive preorder traversal # # tree.middle_travel (tree.root) # recursive preorder tree.last_travel (tree.root) # after the recursive preorder traversal Print ( " --- " * 20 ) # front tree.front () # stack preorder # tree.middle () # stack preorder tree.last () # stacker is preorder
to sum up:
Summed up what the binary tree construction and traversal, look at the online reference other blog, some blog is very well written, but more blog algorithms or verbose, or code quality is not high, very laborious to read, so he re-write again. After which the stack order traversal little trouble, a bit difficult to understand, the proposed map drawn look on paper.