Binary tree is traversed normal operation, this is one of the basic skills of a binary tree
class TreeNode(): def __init__(self, x): self.val = x self.left = None self.right = None class BinaryTree(object): def __init__(self, pre, tin): self.pre = pre self.tin = Tin self.levelTrave = [] # hierarchy traversal results self.preTraveRecur = [] # preamble recursive traversal results self.preTraveNoRecur = [] # preamble non-recursive traversal results self.inTraveRecur = [] # in order recursive traversal results self.inTraveNoRecur = [] # in order non-recursive traversal results self.postTraveRecur = [] # postorder recursive traversal results self.postTraveNoRecur = [] # post-order non-recursive traversal results # Before use preorder traversal results and reconstructed binary sequence DEF reConstructBinaryTree (Self, pre, tin): # pre result of a preorder traversal, tin preorder result IF len (pre) == 0: return None IF len ( pre) ==. 1 : return the TreeNode (pre [0]) the else : res = TreeNode(pre[0]) res.left = self.reConstructBinaryTree(pre[1:tin.index(pre[0]) + 1], tin[:tin.index(pre[0])]) res.right = self.reConstructBinaryTree(pre[tin.index(pre[0]) + 1:], tin[tin.index(pre[0]) + 1:]) return res # Traverse the level DEF levelTraversal (Self, PROOT): aux = [] IF PROOT = None:! # non-empty root node is added to the list aux aux = [PROOT] the while len (aux): # determine whether there are elements aux list, if there are elements continue to visit, or to traverse the end of the p-aux.pop = (0) # Analog queue each time to take the first element of the list self.levelTrave.append (p. Val) IF p.left = None:! # if the current element has left the first node to join aux end of the list aux.append (p.left) IF p.right = None:! # If the current first element has to be the right node Join aux end of the list aux.append (p.right) # Pre-order recursive traversal DEF preorderTraversalRecursion (Self, PROOT): IF PROOT == None: return self.preTraveRecur.append (pRoot.val) # ! ! ! ! ! ! ! IF pRoot.left =! None: self.preorderTraversalRecursion(pRoot.left) if pRoot.right != None: self.preorderTraversalRecursion(pRoot.right) # Preamble non-recursive traversal DEF preorderTraversalNoRecursion (Self, PROOT): IF PROOT == None: return AUX = [] the Node = PROOT the while the Node or the AUX: the while the Node: # starting from the root, has been looking for its left subtree self.preTraveNoRecur.append (node.val) aux.append (node) node = node.left # the while end node indicates that the current node is empty, that before a tree node has no left child of node = aux.pop () # start looking at it right subtree node = node.right # In order recursive traversal DEF inorderTraversalRecursion (Self, PROOT): IF PROOT == None: return IF ! PRoot.left = None: self.inorderTraversalRecursion(pRoot.left) self.inTraveRecur.append(pRoot.val) # ！！！！！！！！ if pRoot.right != None: self.inorderTraversalRecursion(pRoot.right) # The non-recursive traversal sequence DEF inorderTraversalNoRecursion (Self, PROOT): IF the root == None: return AUX = [] the Node = root the while the Node or the AUX: the while the Node: # starting from the root, has been found in the left subtree aux.append (node) node = node.left # the while end node indicates that the current node is empty, that before a tree node has no left child of node = aux.pop () self.inTraveNoRecur.append(node.val) node = node.right # Postorder traversal recursion DEF postorderTraversalRecursion (Self, PROOT): IF PROOT == None: return IF ! PRoot.left = None: self.postorderTraversalRecursion(pRoot.left) if pRoot.right != None: self.postorderTraversalRecursion(pRoot.right) self.postTraveRecur.append(pRoot.val) # ！！！！！！ # The non-recursive traversal sequence DEF postorderTraversalNoRecursion (Self, PROOT): IF the root == None: return AUX = [] the Node = root the while the Node or the AUX: the while the Node: # starting from the root, has been looking for its right subtree self.postTraveNoRecur.insert (0, node.val) aux.append (node) node = node.right # the while end node indicates that the current node is empty, that before a node does not have the right child node = aux.pop () # start viewing its left sub-tree node = node.left IF the __name__ == ' __main__ ' : # using the preamble and the reconstructed binary preorder pre = [. 1, 2,. 4,. 7,. 3,. 5,. 6,. 8 ] message = [4, 7, 2, 1, 5, 3, 8, 6 ] BT = BinaryTree (for, tin) root = BT.reConstructBinaryTree (BT.pre, BT.tin) # Traverse the level BT.levelTraversal (root) Print ( " level through the results: " , BT.levelTrave) # Pre-order recursive traversal BT.preorderTraversalRecursion (root) Print ( " pre-order recursive traversal: " , BT.preTraveRecur) # Preamble non-recursive traversal BT.preorderTraversalNoRecursion (root) Print ( " preamble non-recursive traversal: " , BT.preTraveNoRecur) # In order recursive traversal BT.inorderTraversalRecursion (root) Print ( " in order recursive traversal: " , BT.inTraveRecur) # The non-recursive traversal order BT.inorderTraversalNoRecursion (the root) Print ( " the non-recursive traversal order " , BT.inTraveNoRecur) # Order recursive traversal after BT.postorderTraversalRecursion (root) Print ( " post-order recursive traversal " , BT.postTraveRecur) # Sequence after non-recursive traversal BT.postorderTraversalNoRecursion (the root) Print ( " postorder traversal non-recursive " , BT.postTraveNoRecur)