leetcode-94-binary tree inorder traversal

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

For example:
Given binary tree {1,#,2,3},
1

2
/
3
return [1,3,2].

中序遍历一个二叉树

用递归的办法做很简单，这里选择一个辅助栈，用非递归的方法完成中序遍历。

/**
 * 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) {
            stack<TreeNode*> s;
            vector<int> res;
            while(!s.empty()||root)
                {
                    s.push(root);
                    while(root->left)
                        {
                            s.push(root->left);
                            root=root->left;
                        }
                    while(!s.empty())
                        {
                            root=s.top();
                            s.pop();
                            res.push_back(root->val);
                    if(root->right)
                        {
                            root=root->right;
                            break;
                        }else root=NULL;
                        }
                }
            return res;

        }
    };