题目:Binary Tree Postorder Traversal
二叉树的后序遍历,题目要求是采用非递归的方式,这个在上数据结构的课时已经很清楚了,二叉树的非递归遍历不管采用何种方式,都需要用到栈结构作为中转,代码很简单,见下:
1 struct TreeNode {
2 int val;
3 TreeNode* left;
4 TreeNode* right;
5 TreeNode(int x): val(x), left(NULL),right(NULL) {}
6 };
7
8 vector<int> preorderTraversal(TreeNode *root) //非递归的后序遍历(用栈实现)
9 {
10 if (NULL == root) {
11 return vector<int>();
12 }
13
14 stack<TreeNode *> tree_stack;
15 vector<int> tree_vector;
16
17 tree_stack.push(root);
18 TreeNode *p = NULL;
19 while (!tree_stack.empty()) {
20 TreeNode *pTemp = tree_stack.top();
21 if ((pTemp->left == NULL && pTemp->right == NULL) || ((p != NULL) && (pTemp->left == p || pTemp->right == p))) {
22 tree_vector.push_back(pTemp->val);
23 tree_stack.pop();
24
25 p = pTemp;
26 }
27 else {
28 while(pTemp) {
29 if (pTemp->right != NULL)
30 tree_stack.push(pTemp->right);
31
32 if (pTemp->left != NULL)
33 tree_stack.push(pTemp->left);
34 pTemp = pTemp->left;
35 }
36 }
37 }
38 return tree_vector;
39 }