[Leetcode] 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].

Recursion

class Solution {
private:
    vector<int> result;
public:
    vector<int> inorderTraversal(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        result.clear();        
        if(!root) return result;        
        inorderTrav(root);          
        return result;         
    }
    
    void inorderTrav(TreeNode *root)
    {
        if(root->left) inorderTrav(root->left);
        result.push_back(root->val);
        if(root->right) inorderTrav(root->right);
    }
};

Iteration

class Solution {
public:
    vector<int> inorderTraversal(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> result;
        if(!root) return result;
        
        stack<TreeNode*> stk;
        TreeNode* p = root;
        
        do
        {
            if(p!=NULL)
            {
                stk.push(p);
                p=p->left;
            }
            else
            {
                p=stk.top();
                result.push_back(p->val);
                stk.pop();
                p=p->right;
            }          
        }while(!stk.empty()||p!=NULL); //注意判断条件 
        
        return result;
              
    }
    
};