标签：code 注意 inpu init binary treenode node val 距离
问题：
给定一棵二叉树。
求给定节点target开始，距离K的所有节点。
Example 1: Input: root = [3,5,1,6,2,0,8,null,null,7,4], target = 5, K = 2 Output: [7,4,1] Explanation: The nodes that are a distance 2 from the target node (with value 5) have values 7, 4, and 1. Note that the inputs "root" and "target" are actually TreeNodes. The descriptions of the inputs above are just serializations of these objects. Note: The given tree is non-empty. Each node in the tree has unique values 0 <= node.val <= 500. The target node is a node in the tree. 0 <= K <= 1000.
解法：DFS+BFS
思想：
?? 注意：对于每个父节点，需要知道的信息为自己应该向下遍历的K应该是多少。
因此DFS返回K值。
代码参考：
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 void bfs(vector<int>& res, TreeNode* root, int K) { 13 queue<TreeNode*> q; 14 q.push(root); 15 if(K<0) return; 16 while(!q.empty()) { 17 int sz = q.size(); 18 for(int i=0; i<sz; i++) { 19 TreeNode* cur = q.front(); 20 q.pop(); 21 if(K==0) res.push_back(cur->val); 22 if(cur->left) q.push(cur->left); 23 if(cur->right) q.push(cur->right); 24 } 25 if(K==0) return; 26 K--; 27 } 28 return; 29 } 30 int dfs(vector<int>& res, TreeNode* root, TreeNode* target, int K) { 31 if(!root) return INT_MAX; 32 int left = INT_MAX, right = INT_MAX; 33 if(root->val == target->val) { 34 bfs(res, root, K); 35 return K-1; 36 } else { 37 if(root->left) left = dfs(res, root->left, target, K); 38 if(left==INT_MAX && root->right) right = dfs(res, root->right, target, K); 39 } 40 if(left!=INT_MAX) { 41 if(left==0)res.push_back(root->val); 42 else if(root->right) bfs(res, root->right, left-1); 43 return left-1; 44 } else if(right!=INT_MAX) { 45 if(right==0)res.push_back(root->val); 46 else if(root->left)bfs(res, root->left, right-1); 47 return right-1; 48 } 49 return INT_MAX; 50 } 51 vector<int> distanceK(TreeNode* root, TreeNode* target, int K) { 52 vector<int> res; 53 dfs(res, root, target, K); 54 return res; 55 } 56 };
863. All Nodes Distance K in Binary Tree
标签：code 注意 inpu init binary treenode node val 距离
原文地址：https://www.cnblogs.com/habibah-chang/p/14498823.html
