<p>You are given the <code>root</code> of a binary tree and an integer <code>distance</code>. A pair of two different <strong>leaf</strong> nodes of a binary tree is said to be good if the length of <strong>the shortest path</strong> between them is less than or equal to <code>distance</code>.</p>

<p>Return <em>the number of good leaf node pairs</em> in the tree.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/07/09/e1.jpg" style="width: 250px; height: 250px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,null,4], distance = 3
<strong>Output:</strong> 1
<strong>Explanation:</strong> The leaf nodes of the tree are 3 and 4 and the length of the shortest path between them is 3. This is the only good pair.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/07/09/e2.jpg" style="width: 250px; height: 182px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,4,5,6,7], distance = 3
<strong>Output:</strong> 2
<strong>Explanation:</strong> The good pairs are [4,5] and [6,7] with shortest path = 2. The pair [4,6] is not good because the length of ther shortest path between them is 4.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> root = [7,1,4,6,null,5,3,null,null,null,null,null,2], distance = 3
<strong>Output:</strong> 1
<strong>Explanation:</strong> The only good pair is [2,5].
</pre>

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

<ul>
	<li>The number of nodes in the <code>tree</code> is in the range <code>[1, 2<sup>10</sup>].</code></li>
	<li><code>1 &lt;= Node.val &lt;= 100</code></li>
	<li><code>1 &lt;= distance &lt;= 10</code></li>
</ul>

/**
 * Definition for a binary tree node.
 * 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:
    int helper(unordered_map<TreeNode*,vector<TreeNode*>>&gr,set<TreeNode*>&leaf,TreeNode*x,int dis)
    {
            queue<pair<TreeNode*,int>>q;
            q.push({x,0});
            set<TreeNode*> vis;  
                    vis.insert(x);

            int ans=0;
            while(!q.empty())
            {
                            auto [top, d] = q.front();
                             q.pop();
                             if(d>dis)
                             {
                                continue;
                             }
                if (leaf.find(top) != leaf.end() && top != x && d <= dis) {
                ans++;
            }
            
            for (auto neighbor : gr[top]) {
                if (vis.find(neighbor) == vis.end()) { 
                    vis.insert(neighbor);
                    q.push({neighbor, d + 1});
                }
            }

            }
            return ans;


        }
    int countPairs(TreeNode* root, int distance) {
        unordered_map<TreeNode*,vector<TreeNode*>>gr;
        
        queue<TreeNode*>q;
        set<TreeNode*>leaf;
        q.push(root);
        while(!q.empty())
        {
            int s=q.size();
            for(int i=0;i<s;i++)
            {
                TreeNode*top=q.front();
                q.pop();
                if(top->left)
                {
                    q.push(top->left);
                    gr[top].push_back(top->left);
                    gr[top->left].push_back(top);
                }
                 if(top->right)
                {
                    q.push(top->right);
                    gr[top].push_back(top->right);
                    gr[top->right].push_back(top);
                }
                if(top->left==NULL && top->right==NULL)
                leaf.insert(top);
            }
        }
        int ans=0;
        for(auto x:leaf)
        ans+=helper(gr,leaf,x,distance);
        return ans/2;




    }
};
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