/** * 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
     
       distanceK(TreeNode* root, TreeNode* target, int K) {        vector
      
        visited(501, false);        vector
       
        
         > g(501);                dfs(root, g);                vector
         
           res;        queue
          
            q; q.push(target->val); visited[target->val] = true; int lv = 0; while (!q.empty()) { int qs = q.size(); if (lv == K) { while(!q.empty()) { res.push_back(q.front()); q.pop(); } break; } while (qs-- > 0) { int p = q.front(); q.pop(); for (auto i : g[p]) { if (!visited[i]) { q.push(i); visited[i] = true; } } } lv++; } return res; } void dfs(TreeNode *root, vector
           
            
             >& g) { if (root == NULL) return; if (root->left) { g[root->val].insert(root->left->val); g[root->left->val].insert(root->val); } if (root->right) { g[root->val].insert(root->right->val); g[root->right->val].insert(root->val); } dfs(root->left, g); dfs(root->right, g); }};