Create Find Elements in a Contaminated Binary Tree

AAAA-source · web-flow · commit a595e39bfccc · 2025-02-21T20:48:27.000+08:00
diff --git a/Daily Question/2025/February/Find Elements in a Contaminated Binary Tree b/Daily Question/2025/February/Find Elements in a Contaminated Binary Tree
@@ -0,0 +1,44 @@
+想法：用 DFS 的方式重建整棵樹，並用 hash set 紀錄出現過的數字，未來查找時只需查看 hash set 中是否存在即可
+
+Time Complexity : O(n) for constructing n nodes in the tree
+  Space Complexity : O(n) for the hash set to store n numbers
+
+
+/**
+ * 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 FindElements {
+public:
+    unordered_set<int> appear ;
+    void DFS(int x , TreeNode* root) {
+        if ( x > 1e6 || !root )
+            return ;
+        
+        appear.insert(x) ;
+        //cout << "insert : " << x << endl ;
+        DFS(2 * x + 1 , root->left) ;
+        DFS(2 * x + 2 , root->right) ;
+        return ;
+    }
+    FindElements(TreeNode* root) {
+        DFS(0 , root) ;
+    }
+    
+    bool find(int target) {
+        return appear.find(target) != appear.end() ;
+    }
+};
+
+/**
+ * Your FindElements object will be instantiated and called as such:
+ * FindElements* obj = new FindElements(root);
+ * bool param_1 = obj->find(target);
+ */
