leetcode-----94. 二叉树的中序遍历

• 链接：https://leetcode-cn.com/problems/binary-tree-inorder-traversal/

代码

/**
 * 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> ans;
        stack<TreeNode*> stk;

        while (root || stk.size()) {
            while (root) {
                stk.push(root);
                root = root->left;
            }
            root = stk.top();
            stk.pop();
            ans.push_back(root->val);
            root = root->right;
        }
        return ans;
    }
};