number of good leafs.cpp

class Solution {
public:
    int countPairs(TreeNode* root, int distance) {
        unordered_map<TreeNode*, vector<TreeNode*>> map;
        vector<TreeNode*> leaves;
        findLeaves(root, {}, leaves, map);
        int res = 0;
        for (int i = 0; i < leaves.size(); i++) {
            for (int j = i + 1; j < leaves.size(); j++) {
                vector<TreeNode*>& list_i = map[leaves[i]];
                vector<TreeNode*>& list_j = map[leaves[j]];
                for (int k = 0; k < min(list_i.size(), list_j.size()); k++) {
                    if (list_i[k] != list_j[k]) {
                        int dist = list_i.size() - k + list_j.size() - k;
                        if (dist <= distance) res++;
                        break;
                    }
                }
            }
        }
        return res;
    }

private:
    void findLeaves(TreeNode* node, vector<TreeNode*> trail, vector<TreeNode*>& leaves, unordered_map<TreeNode*, vector<TreeNode*>>& map) {
        if (!node) return;
        vector<TreeNode*> tmp(trail);
        tmp.push_back(node);
        if (!node->left && !node->right) {
            map[node] = tmp;
            leaves.push_back(node);
            return;
        }
        findLeaves(node->left, tmp, leaves, map);
        findLeaves(node->right, tmp, leaves, map); 
    }
};