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Author: assassint2017

Kth Smallest Element in a BST/Kth_Smallest_Element_in_a_BST.cpp

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+// Runtime: 20 ms, faster than 84.89% of C++ online submissions for Kth Smallest Element in a BST.
+// Memory Usage: 21.5 MB, less than 72.76% of C++ online submissions for Kth Smallest Element in a BST.
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Solution 
+{
+public:
+    int kthSmallest(TreeNode* root, int k) 
+	{
+		stack<TreeNode*> treeStack;
+		while (true)
+		{
+			while (root)
+			{
+				treeStack.push(root);
+				root = root->left;
+			}
+			if (!treeStack.empty())
+			{
+				root = treeStack.top();
+				treeStack.pop();
+
+				if (k == 1)
+					break;
+				else
+					--k;
+				
+				root = root->right;
+			}
+		}
+		return root->val;
+    }
+};