<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:
    vector<int> distanceK(TreeNode* root, TreeNode* target, int k) {
    map<TreeNode*, TreeNode*> parentNodeMap;
     Storeparent(root,nullptr,parentNodeMap);

     queue<pair<TreeNode*,int>> q;
     unordered_set<TreeNode*> visited;
     vector<int> result;

     if(root==nullptr){
        return result;
     }
     q.push({target,0});
      visited.insert(target);

      while(!q.empty()){
         auto[node,dis]=q.front();
         q.pop();

         if(dis==k){
            result.push_back(node->val);
         }
         if(dis>k){
            break;
         }
         if(node->left && visited.find(node->left)==visited.end()){
            q.push({node->left,dis+1});
            visited.insert(node->left);
         }
          if(node->right && visited.find(node->right)==visited.end()){
            q.push({node->right,dis+1});
            visited.insert(node->right);
         }

         if(parentNodeMap[node] && visited.find(parentNodeMap[node])==visited.end()){
            q.push({ parentNodeMap[node],dis+1});
            visited.insert( parentNodeMap[node]);
         }

      }   
    return result;
        
    }

    
private:  void Storeparent(TreeNode* root,TreeNode* parent,map<TreeNode*, TreeNode*> &parentNodeMap ){
    if(root==nullptr){
        return;
    }
     parentNodeMap[root]=parent;


    Storeparent(root->left,root,parentNodeMap);
    Storeparent(root->right,root,parentNodeMap);
}
};
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