problem 98

ValidateBinarySearchTree.cpp

@@ -0,0 +1,44 @@
+#include <bits/stdc++.h>
+
+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) {
+        if (root != nullptr) {
+            return valid(root, INT_MIN, INT_MAX, false, false);
+        }
+        else {
+            return true;
+        }
+    }
+    bool valid(TreeNode* t, int min, int max, bool wasMin, bool wasMax) {
+        if ((wasMin && t->val <= min) || (wasMax && t->val >= max)) {
+            return false;
+        }
+        if (t->left != nullptr) {
+            bool l = valid(t->left, min, t->val, wasMin, true);
+            if (t->right != nullptr) {
+                return l && valid(t->right, t->val, max, true, wasMax);
+            }
+            else {
+                return l;
+            }
+        }
+        else {
+            if (t->right != nullptr) {
+                return valid(t->right, t->val, max, true, wasMax);
+            }
+            else {
+                return true;
+            }
+        }
+    }
+};