LeetCode94:二叉树的中序遍历(Binary Tree Inorder Traversal)

英文题目：

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

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,3,2]

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

中文题目：

给定一个二叉树，返回它的中序 遍历。

示例:

输入: [1,null,2,3]
   1
    \
     2
    /
   3

输出: [1,3,2]

进阶: 递归算法很简单，你可以通过迭代算法完成吗？

解答：

C++

/**
 * Definition for a binary tree node.
 * 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) {
        vector<int> res;
        stack<TreeNode*> stk;
        
        auto p=root;
        while (p || stk.size())
        {
            while (p)
            {
                stk.push(p);
                p = p->left;
            }
            p = stk.top();
            stk.pop();
            res.push_back(p->val);
            p=p->right;
        }
        return res;
    }
};

来源：https://blog.csdn.net/XB_please/article/details/100855085