Leetcode Binary Tree Inorder Traversal

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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].

Note: Recursive solution is trivial, could you do it iteratively?

confused what "{1,#,2,3}" means? 

遞迴解決方案

class Solution {public:    vector<int> res;        void inorder(TreeNode* root){        if(root == NULL) return;        inorder(root->left);        res.push_back(root->val);        inorder(root->right);    }        vector<int> inorderTraversal(TreeNode *root) {        inorder(root);        return res;    }};

遞迴中序遍曆

 非遞迴解決方案

class Solution {public:    vector<int> inorderTraversal(TreeNode *root) {        vector<int> res;        if(root == NULL) return res;        stack<TreeNode *> nodeStack;        TreeNode *current = root;        while(!nodeStack.empty() || current ){            if(current != NULL){                nodeStack.push(current);                current = current->left;            }else{                current = nodeStack.top();nodeStack.pop();                res.push_back(current->val);                current = current->right;            }        }        return res;    }};

非遞迴中序遍曆