LeetCode: Binary Tree Inorder Traversal

LeetCode: Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

地址：https://oj.leetcode.com/problems/binary-tree-inorder-traversal/

算法：要求用非递归来进行中序遍历。初始时，从根节点开始，一直往左走，并把每个节点入栈。在while循环内，取栈顶元素，出栈，访问该元素，若该元素有右孩子，往右走，在一直往左走到低并把每个节点进栈，如此循环知道栈为空。代码：

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<int> inorderTraversal(TreeNode *root) {
13         vector<int> result;
14         if(!root)   return result;
15         TreeNode *p = root;
16         stack<TreeNode*> stk;
17         while(p){
18             stk.push(p);
19             p = p->left;
20         }
21         while(!stk.empty()){
22             p = stk.top();
23             stk.pop();
24             result.push_back(p->val);
25             p = p->right;
26             while(p){
27                 stk.push(p);
28                 p = p->left;
29             }
30         }
31         return result;
32     }
33 };