94.binary-tree-inorder-traversal.cpp

/*
 * @lc app=leetcode id=94 lang=cpp
 *
 * [94] Binary Tree Inorder Traversal
 *
 * https://leetcode.com/problems/binary-tree-inorder-traversal/description/
 *
 * algorithms
 * Easy (72.01%)
 * Likes:    9061
 * Dislikes: 424
 * Total Accepted:    1.7M
 * Total Submissions: 2.3M
 * Testcase Example:  '[1,null,2,3]'
 *
 * Given the root of a binary tree, return the inorder traversal of its nodes'
 * values.
 *
 *
 * Example 1:
 *
 *
 * Input: root = [1,null,2,3]
 * Output: [1,3,2]
 *
 *
 * Example 2:
 *
 *
 * Input: root = []
 * Output: []
 *
 *
 * Example 3:
 *
 *
 * Input: root = [1]
 * Output: [1]
 *
 *
 *
 * Constraints:
 *
 *
 * The number of nodes in the tree is in the range [0, 100].
 * -100 <= Node.val <= 100
 *
 *
 *
 * Follow up: Recursive solution is trivial, could you do it iteratively?
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution
{
public:
    vector<int> inorderTraversal(TreeNode *root, vector<int> *ans = new vector<int>())
    {

        if (root == nullptr)
            return *ans;
        inorderTraversal(root->left, ans);
        ans->push_back(root->val);
        inorderTraversal(root->right, ans);
        return *ans;
    }
};
// @lc code=end