4: kth smallest element in a bst

Author: whewchews

kth-smallest-element-in-a-bst/whewchews.ts

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+function kthSmallest(root: TreeNode | null, k: number): number {
+  // SC: O(N)
+  const values: number[] = [];
+
+  // TC: O(N)
+  const dfs = (node: TreeNode | null) => {
+    if (node == null) return;
+    dfs(node.left);
+    values.push(node.val);
+    dfs(node.right);
+  };
+
+  // SC: O(h)
+  // h: the height of the tree
+  dfs(root);
+
+  // TC: O(1)
+  return values[k - 1];
+}
+
+// TC: O(N)
+// SC: O(N)