k-th smallest element in BST

Author: sachuverma

DSA Crack Sheet/README.md

@@ -212,6 +212,7 @@
 - [Convert a normal BST to Balanced BST](https://www.geeksforgeeks.org/convert-normal-bst-balanced-bst/ "view topic")
 - [Merge Two Balanced Binary Search Trees](https://www.geeksforgeeks.org/merge-two-balanced-binary-search-trees/ "view post")
 - [Kth largest element in BST](https://practice.geeksforgeeks.org/problems/kth-largest-element-in-bst/1# "view question") - [Cpp Solution](./solutions/Kth%20largest%20element%20in%20BST.cpp)
+- [k-th smallest element in BST](https://practice.geeksforgeeks.org/problems/find-k-th-smallest-element-in-bst/1 "view question") - [Cpp Solution](./solutions/k-th%20smallest%20element%20in%20BST.cpp)
 - []( "view question") - [Cpp Solution](./solutions/.cpp)
 
 ### Greedy Method

DSA Crack Sheet/solutions/k-th smallest element in BST.cpp

@@ -0,0 +1,55 @@
+/*
+k-th smallest element in BST
+============================
+
+Given a BST and an integer K. Find the Kth Smallest element in the BST. 
+
+Example 1:
+Input:
+      2
+    /   \
+   1     3
+K = 2
+Output: 2
+
+Example 2:
+Input:
+        2
+      /  \
+     1    3
+K = 5
+Output: -1
+ 
+
+Your Task:
+You don't need to read input or print anything. Your task is to complete the function KthSmallestElement() which takes the root of the BST and integer K as inputs and return the Kth smallest element in the BST, if no such element exists return -1.
+
+Expected Time Complexity: O(N).
+Expected Auxiliary Space: O(1).
+
+Constraints:
+1<=Number of nodes<=100000
+*/
+
+int ans = -1;
+void inorder(Node *root, int &k)
+{
+  if (k == 0 || !root)
+    return;
+  inorder(root->left, k);
+  k--;
+  if (k == 0)
+  {
+    ans = root->data;
+    return;
+  }
+  inorder(root->right, k);
+}
+
+// Return the Kth smallest element in the given BST
+int KthSmallestElement(Node *root, int K)
+{
+  //add code here.
+  inorder(root, K);
+  return ans;
+}