94.binary-tree-inorder-traversal.cpp

#include<vector>
using namespace std;
/*
 * @lc app=leetcode id=94 lang=cpp
 *
 * [94] Binary Tree Inorder Traversal
 *
 * https://leetcode.com/problems/binary-tree-inorder-traversal/description/
 *
 * algorithms
 * Medium (61.17%)
 * Likes:    2574
 * Dislikes: 112
 * Total Accepted:    647.2K
 * Total Submissions: 1.1M
 * Testcase Example:  '[1,null,2,3]'
 *
 * Given a binary tree, return the inorder traversal of its nodes' values.
 * 
 * Example:
 * 
 * 
 * Input: [1,null,2,3]
 * ⁠  1
 * ⁠   \
 * ⁠    2
 * ⁠   /
 * ⁠  3
 * 
 * Output: [1,3,2]
 * 
 * Follow up: Recursive solution is trivial, could you do it iteratively?
 * 
 */
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

// @lc code=start
/**
 * 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> res;
    vector<int> inorderTraversal(TreeNode *root) {
        res = vector<int>();
        inorder(root);
        return res;
    }
    void inorder(TreeNode *root) {
        if (root == nullptr) return ;
        inorder(root->left);
        res.push_back(root->val);
        inorder(root->right);
    }
};
// @lc code=end