[面试真题] LeetCode：Binary Tree Inorder Traversal

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

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

二叉树中序遍历，非递归解法。使用栈记录中序遍历时中间节点的访问顺序，从栈中弹出的顺序即为中序。

Program Runtime: 16 milli secs

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> rtn;
        if(root){
            stack<TreeNode*> s;
            s.push(root);
            TreeNode *p = root;
            while(p->left){
               s.push(p->left);
              p = p->left;
             }
            while(s.size()){
                TreeNode *cur = s.top();
                s.pop();
                rtn.push_back(cur->val);
                if(cur->right){
                    s.push(cur->right);
                    cur = cur->right;
                    while(cur->left){
                        s.push(cur->left);
                        cur = cur->left;
                    }
                }
            }
        }
        return rtn;
    }
};