二叉树遍历94. Binary Tree Inorder Traversal

/** * 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* > nodeStack;        TreeNode* current = root;        if (root == NULL)            return ans;        while (nodeStack.size() || current != NULL)        {            while (current != NULL)            {                nodeStack.push(current);                current = current->left;            }            if (!nodeStack.empty())            {                current = nodeStack.top();                nodeStack.pop();                ans.push_back(current->val);                current = current->right;            }        }        return ans;    }};