Added Solution of LeetCode Problem No. 230

Domains/CompetitiveProgramming/Programs/C/LeetCode/Q230.c

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+/*
+===============================================================
+230. Kth Smallest Element in a BST
+===============================================================
+
+Difficulty: Medium
+Tags: Binary Search Tree, Depth-First Search, Tree, Binary Tree
+
+---------------------------------------------------------------
+Problem Statement:
+---------------------------------------------------------------
+Given the root of a binary search tree (BST) and an integer k,
+return the kth smallest value (1-indexed) among all the values
+of the nodes in the tree.
+
+---------------------------------------------------------------
+Example 1:
+---------------------------------------------------------------
+Input: root = [3,1,4,null,2], k = 1
+Output: 1
+
+Explanation:
+The in-order traversal of the BST is [1, 2, 3, 4].
+The 1st smallest element is 1.
+
+---------------------------------------------------------------
+Example 2:
+---------------------------------------------------------------
+Input: root = [5,3,6,2,4,null,null,1], k = 3
+Output: 3
+
+Explanation:
+The in-order traversal of the BST is [1, 2, 3, 4, 5, 6].
+The 3rd smallest element is 3.
+
+---------------------------------------------------------------
+Constraints:
+---------------------------------------------------------------
+- The number of nodes in the tree is n.
+- 1 <= k <= n <= 10^4
+- 0 <= Node.val <= 10^4
+
+---------------------------------------------------------------
+Hint:
+---------------------------------------------------------------
+- The in-order traversal of a BST gives the elements
+  in sorted order.
+- You can stop traversing early once you reach the kth element.
+===============================================================
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     struct TreeNode *left;
+ *     struct TreeNode *right;
+ * };
+ */
+
+/**
+ * Function: inorder
+ * -----------------
+ * Performs an in-order traversal of the BST to find the kth smallest element.
+ * 
+ * @param p     : Pointer to the current node in the BST.
+ * @param k     : The target position (kth smallest element to find).
+ * @param temp  : Temporary variable to store the current result.
+ * 
+ * @return      : The kth smallest value if found, otherwise returns temp.
+ */
+
+
+int inorder(struct TreeNode* p, int k, int temp)
+{
+    // Base case: if the current node is NULL, simply return temp
+    if (p != NULL)
+    {
+        // Traverse the left subtree first (smallest elements come first in BST)
+        temp = inorder(p->left, k - 1, temp);
+
+        // If k reaches 0, we have found the kth smallest node
+        if (k == 0)
+        {
+            return p->val;
+        }
+
+        // Continue traversal in the right subtree
+        temp = inorder(p->right, k - 1, temp);
+    }
+
+    // Return the temporary result if kth element is not found yet
+    return temp;
+}