<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) {}
 * };
 */
class Solution {
public:
    void dfs(TreeNode* root,map<TreeNode*,TreeNode*>&par,TreeNode* parent){
             if(!root)
        return;
        par[root]=parent;
  

        dfs(root->left,par,root);
        dfs(root->right,par,root);
    }
    vector<int> distanceK(TreeNode* root, TreeNode* target, int k) {

        map<TreeNode*,TreeNode*>par;
        dfs(root,par,NULL);

        queue<TreeNode*>q;
        q.push(target);
        map<TreeNode*,int>vis;

        vis[target]=1;
        int d=0;
        vector<int>res;

        while(!q.empty()){
            int sz=q.size();
            while(sz--){
                auto u=q.front();
                q.pop();
                if(d==k)
                res.push_back(u->val);
                vis[u]=1;
                if(u->left&&vis.find(u->left)==vis.end()){
                    q.push(u->left);
                }
                 if(par[u]&&vis.find(par[u])==vis.end()){
                    q.push(par[u]);
                }
                 if(u->right&&vis.find(u->right)==vis.end()){
                    q.push(u->right);
                }
            }
            if(d>=k){
                break;
            }
            d++;

        }
        return res;
        
    }
};
16000