leetcode

数据结构与算法/算法题总结.md

@@ -12651,6 +12651,68 @@ private:
 };
 ```
 
+以树构建graph（节点与左右子节点连通），然后从target节点开始以BFS的方式遍历graph，深度为K的节点就是结果：
+```
+/**
+ * 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<int> distanceK(TreeNode* root, TreeNode* target, int k) {
+        unordered_map<TreeNode*, vector<TreeNode*> > m;
+        buildGraph(root, m);
+
+        deque<TreeNode *> res;
+        res.push_back(target);
+
+        while(k && !res.empty()) {
+            int sz = res.size();
+            --k;
+            for (int i = 0; i < sz; i++) {
+                TreeNode *nd = res.front();
+                res.pop_front();
+
+                for (TreeNode *next : m[nd]) {
+                    if (m.find(next) != m.end()) {
+                        res.push_back(next);
+                    }
+                }
+                m.erase(nd); // remove visited node
+            }
+        }
+
+        vector<int> res_values(res.size());
+        for (int i = 0; i < res.size(); i++) {
+            res_values[i] = res[i]->val;
+        }
+        return res_values;
+    }
+private:
+    void buildGraph(TreeNode *nd, unordered_map<TreeNode*, vector<TreeNode*> > &m) {
+        if (!nd) {
+            return;
+        }
+
+        if (nd->left) {
+            m[nd].push_back(nd->left);
+            m[nd->left].push_back(nd);
+            buildGraph(nd->left, m);
+        }
+        if (nd->right) {
+            m[nd].push_back(nd->right);
+            m[nd->right].push_back(nd);
+            buildGraph(nd->right, m);
+        }
+    }
+};
+```
+
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