98. Validate Binary Search Tree

Author: SjxSubham

98. Validate Binary Search Tree

@@ -0,0 +1,28 @@
+class Solution {
+public:
+
+// T. c - O(n)
+// n times reverse kar rahe hai, isliye
+
+    bool solve(TreeNode* root,long long int lowerBound,long long int upperBound){
+        if(root == NULL){
+            return true;
+        }
+        bool cond1 = (root->val > lowerBound);
+        bool cond2= (root->val < upperBound);
+        bool leftAns = solve(root->left, lowerBound,root->val);
+        bool rightAns = solve(root->right,root->val,upperBound);
+
+        if( cond1 && cond2 && leftAns && rightAns)
+            return true;
+        else
+            return false;
+    }
+    bool isValidBST(TreeNode* root) {
+        
+        long long int lowerBound = -2147483657;  // we have to increase the limit
+        long long int upperBound = 2147483657;  // we have to increase the limit  
+        bool ans = solve(root,lowerBound,upperBound);
+       return ans;
+    
+};