# Binary Tree Postorder Traversal Problem & Solution

Given the `root` of a binary tree, return the postorder traversal of its nodes' values.

## C++ Solution

``````#pragma GCC optimize("Ofast")
#pragma GCC optimization("max-inline-insns-recursive-auto")

static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

/**
* 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> postorderTraversal(TreeNode* root) {
vector<int> traversal;

postorderTraversal(root, traversal);

return traversal;
}

private:
void postorderTraversal(TreeNode* node, vector<int>& traversal) {
if (node == nullptr) {
return;
}

postorderTraversal(node->left, traversal);
postorderTraversal(node->right, traversal);
traversal.push_back(node->val);
}
};
``````