二叉树中序遍历（非递归）

 

/**
 * 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> re;
        stack<TreeNode*> S;
        TreeNode* p=root;
        while(p||!S.empty()){
            if(p){
                S.push(p);
                p=p->left;
            }else{
                p=S.top();
                S.pop();
                re.emplace_back(p->val);
                p=p->right;
            }
        }
        return re;
    }
};