# Binary Tree Inorder Traversal Problem

## Description

LeetCode Problem 94.

Given the root of a binary tree, return the inorder traversal of its nodes’ values.

Example 1:

``````1
2
Input: root = [1,null,2,3]
Output: [1,3,2]
``````

Example 2:

``````1
2
Input: root = []
Output: []
``````

Example 3:

``````1
2
Input: root = [1]
Output: [1]
``````

Example 4:

``````1
2
Input: root = [1,2]
Output: [2,1]
``````

Example 5:

``````1
2
Input: root = [1,null,2]
Output: [1,2]
``````

Constraints:

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

## Sample C++ Code

``````1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
class Solution {
public:
vector<int> inorderTraversal(TreeNode* root) {
vector<int> nodes;
inorder(root, nodes);
return nodes;
}

void inorder(TreeNode* root, vector<int>& nodes) {
if (!root) {
return;
}
inorder(root -> left, nodes);
nodes.push_back(root -> val);
inorder(root -> right, nodes);
}
};
``````
``````1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
class Solution {
public:
vector<int> inorderTraversal(TreeNode* root) {
vector<int> nodes;
stack<TreeNode*> todo;
while (root || !todo.empty()) {
while (root) {
todo.push(root);
root = root -> left;
}
root = todo.top();
todo.pop();
nodes.push_back(root -> val);
root = root -> right;
}
return nodes;
}
};
``````