非递归的中序遍历(inorder)树 leetcode 94

 1 class Solution {
 2 public:
 3     vector<int> inorderTraversal(TreeNode* root) {
 4         stack<TreeNode*> s;
 5         vector<int> val;
 6         TreeNode* curr = root;
 7         s.push(curr);
 8         while(!s.empty()) {
 9             while(curr) {
10                 s.push(curr->left);
11                 curr = curr->left;
12             }
13             curr = s.top();
14             s.pop();
15             if (curr) {
16                 val.push_back(curr->val);
17                 curr = curr->right;
18                 if (curr) s.push(curr);
19             }
20         }
21         return val;
22     }
23 };