2주차 문제 풀이 1개 추가

- Validate Binary Search Tree

Author: hwi-middle

validate-binary-search-tree/hwi-middle.cpp

@@ -0,0 +1,46 @@
+/**
+ * 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 Solution {
+public:
+    bool isValidBST(TreeNode* root) {
+        vector<int> v;
+        v.reserve(1e4);
+        
+        solve(root, v);
+
+        int len = v.size();
+        for (int i = 0; i < len - 1; ++i)
+        {
+            if (v[i] >= v[i + 1])
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    void solve(TreeNode* root, vector<int>& v)
+    {
+        if (root->left != nullptr)
+        {
+            solve(root->left, v);
+        }
+
+        v.push_back(root->val);
+
+        if (root->right != nullptr)
+        {
+            solve(root->right, v);
+        }
+    }
+};