diff --git a/Easy/NextGreaterElement.cpp b/Easy/NextGreaterElement.cpp
new file mode 100644
index 0000000..f559787
--- /dev/null
+++ b/Easy/NextGreaterElement.cpp
@@ -0,0 +1,31 @@
+//he next greater element of some element x in an array is the first greater element that is to the right of x in the same array
+
+#include <bits.stdc++.h>
+using namespace std
+class Solution {
+public:
+    vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
+        vector<int> ans;
+
+        for(int i =0; i<nums1.size(); i++){
+            int j =0;            
+
+            while(nums1[i]!= nums2[j])
+                j++;        
+
+            int c =0;
+            for(int k = j; k<nums2.size(); k++){
+                if(nums2[j] < nums2[k]){
+                    ans.push_back(nums2[k]);
+                    c++;
+                    break;
+            }
+            }
+			
+               if(c ==0)
+                    ans.push_back(-1);
+            }
+        return ans;
+
+    }
+};
\ No newline at end of file
diff --git a/Medium/ValidBinaryTree.cpp b/Medium/ValidBinaryTree.cpp
new file mode 100644
index 0000000..d4786ea
--- /dev/null
+++ b/Medium/ValidBinaryTree.cpp
@@ -0,0 +1,25 @@
+//Given the root of a binary tree, determine if it is a valid binary search tree (BST).
+
+// 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 helper(TreeNode*root,long min,long max){
+        if(root==NULL)return true;
+        if(root->val<=min || root->val>=max)return false;
+        return helper(root->left,min,root->val)&&helper(root->right,root->val,max);
+        
+    }
+    bool isValidBST(TreeNode* root) {
+        return helper(root,LONG_MIN,LONG_MAX);
+        
+    }
+
+};
\ No newline at end of file