Binary Tree Preorder Traversal

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

Solution With C++

class Solution {

public:

    vector<int>d;

    vector<int> inorderTraversal(TreeNode* root) {

        if(root==NULL) return d;

        d=inorderTraversal(root->left);

        d.push_back(root->val);

        d=inorderTraversal(root->right);

        return d;

    }

};