<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:  unordered_map<TreeNode*,TreeNode*>parent;
void findLeaves(queue<pair<TreeNode*,TreeNode*>>&q, TreeNode*root,TreeNode*par)
{
    if(!root)
    return ;
    parent[root]=par;
    if(!root->left && !root->right)
    { q.push({root,NULL});
    }
    findLeaves(q,root->left,root);
    findLeaves(q,root->right,root);
}
bool isleaf(TreeNode*node)
{
    return !node->left && !node->right;
    }
    int countPairs(TreeNode* root, int distance) {
        queue<pair<TreeNode*,TreeNode*>>q;
      
        if(!root)
        return 0;
        findLeaves(q,root,NULL);
        int cnt=0;
        int dist=0;
        while(!q.empty())
        {
            int size=q.size();
            for(int i=0;i<size;i++)
            { TreeNode*node=q.front().first;
            TreeNode*ancestor=q.front().second;
            q.pop();
                if(dist>=distance)
                {
                    return cnt/2;
                }
                if(node->left && node->left!=ancestor)
                {
                    q.push({node->left,node});

                    if(isleaf(node->left))
                    {
                        cnt++;
                    }
                }
                if(node->right && node->right!=ancestor)
                {
                    q.push({node->right,node});
                    if(isleaf(node->right))
                    {
                        cnt++;
                    }
                }
                if(parent[node] && parent[node]!=ancestor)
                {
                    q.push({parent[node],node});
                    if(isleaf(parent[node]))
                    cnt++;
                }

                
            }
            dist++;

        }
        return cnt/2;
    }
};
45781