<p>Given the <code>root</code> of a binary tree, the value of a target node <code>target</code>, and an integer <code>k</code>, return <em>an array of the values of all nodes that have a distance </em><code>k</code><em> from the target node.</em></p>

<p>You can return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://s3-lc-upload.s3.amazonaws.com/uploads/2018/06/28/sketch0.png" style="width: 500px; height: 429px;" />
<pre>
<strong>Input:</strong> root = [3,5,1,6,2,0,8,null,null,7,4], target = 5, k = 2
<strong>Output:</strong> [7,4,1]
Explanation: The nodes that are a distance 2 from the target node (with value 5) have values 7, 4, and 1.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> root = [1], target = 1, k = 3
<strong>Output:</strong> []
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 500]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 500</code></li>
	<li>All the values <code>Node.val</code> are <strong>unique</strong>.</li>
	<li><code>target</code> is the value of one of the nodes in the tree.</li>
	<li><code>0 &lt;= k &lt;= 1000</code></li>
</ul>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 #pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
static const bool __boost = []() {
	cin.tie(nullptr);
	cout.tie(nullptr);
	return std::ios_base::sync_with_stdio(false);
	}();


const size_t BUFFER_SIZE = 0x6fafffff;
alignas(std::max_align_t) char buffer[BUFFER_SIZE];
size_t buffer_pos = 0;
void* operator new(size_t size) {
	constexpr std::size_t alignment = alignof(std::max_align_t); // Default maximum alignment
	size_t padding = (alignment - (buffer_pos % alignment)) % alignment;
	size_t total_size = size + padding;
	char* aligned_ptr = &buffer[buffer_pos + padding];
	buffer_pos += total_size;
	return aligned_ptr;
}
void operator delete(void* ptr) {
}

// Overload the delete[] operator to do nothing
void operator delete[](void* ptr) {}

#include <execution>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility> 

class Solution {
public:
    unordered_map<int, TreeNode*> parents;
    unordered_map<int, bool> visitedNodes;
    void dfs (TreeNode* root, TreeNode* parent)
    {
        if (root == nullptr)
            return;

        parents[root->val] = parent;
        dfs(root->left, root);
        dfs(root->right, root);
    }

    bool isValid(TreeNode* node)
    {
        return node != nullptr && !visitedNodes[node->val];
    }

    vector<int> distanceK(TreeNode* root, TreeNode* target, int k) 
    {
        vector<int> res;
        dfs(root, nullptr);

        vector<pair<TreeNode*, int>> stack;
        stack.push_back({target, 0});
        visitedNodes[target->val] = true;
        while (stack.size())
        {
            auto fullNode = stack.back();
            auto node = fullNode.first;
            auto depth = fullNode.second;
            stack.pop_back();

            if (depth == k)
            {
                res.push_back(node->val);
                continue;
            }

            auto parent = parents[node->val];
            auto left = node->left;
            auto right = node->right;
            if (isValid(parent))
            {
                stack.push_back({parent, depth + 1});
                visitedNodes[parent->val] = true;;
            }
            if (isValid(left))
            {
                stack.push_back({left, depth + 1});
                visitedNodes[left->val] = true;
            }
            if (isValid(right))
            {
                stack.push_back({right, depth + 1});
                visitedNodes[right->val] = true;
            }
        }

        return res;
    }
};
10000