[LeetCode] 非递归中序遍历二叉树 non recursive inorder traversal

非递归中序遍历二叉树 non recursive inorder traversal 

非递归前序遍历，参看这里。

用两个 while 循环来做, 思路如下.

1) Create an empty stack S.2) Initialize current node as root3) Push the current node to S and set current = current->left until current is NULL4) If current is NULL and stack is not empty then      a) Pop the top item from stack.     b) Print the popped item, set current = popped_item->right      c) Go to step 3.5) If current is NULL and stack is empty then we are done.

下面的代码经过简单修改，可以完成逆中序遍历，即先访问右子树，再访问根节点，最后访问左子树。

    vector<int> inorderTraversal(TreeNode *root) {        vector<int> vec;  // stores the preorder sequence        stack<TreeNode*> st; // auxiliary stack         TreeNode* curr = root;                while(1)        {            while(curr)            {                st.push(curr);                curr = curr->left;            }                        if(st.size()==0)                break;            else            {                curr = st.top();                st.pop();                vec.push_back(curr->val);                curr = curr->right;            }        }                return vec;            }

上面的代码和非递归前序遍历几乎一样。