二刷230

Author: diguage

docs/0230-kth-smallest-element-in-a-bst.adoc

@@ -3,16 +3,6 @@
 
 https://leetcode.com/problems/kth-smallest-element-in-a-bst/[LeetCode - Kth Smallest Element in a BST]
 
-TODO: 树的非递归遍历还需要多加推敲，加强理解。
-
-image::images/0230-1.png[{image_attr}]
-
-image::images/0230-2.png[{image_attr}]
-
-image::images/0230-3.png[{image_attr}]
-
-image::images/0230-4.png[{image_attr}]
-
 Given a binary search tree, write a function `kthSmallest` to find the *k*th smallest element in it.
 
 *Note: *
@@ -55,10 +45,36 @@ You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
 What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?
 
 
+== 思路分析
+
+二叉搜索树的中根遍历是排好序的，所以，求第 K 最小值，直接中根遍历即可。
+
+树的非递归遍历还需要多加推敲，加强理解。
+
+image::images/0230-05.png[{image_attr}]
+
+image::images/0230-01.png[{image_attr}]
+
+image::images/0230-02.png[{image_attr}]
+
+image::images/0230-03.png[{image_attr}]
+
+image::images/0230-04.png[{image_attr}]
 
 [[src-0230]]
 [{java_src_attr}]
 ----
 include::{sourcedir}/_0230_KthSmallestElementInABST.java[tag=answer]
 ----
 
+[[src-0230]]
+[{java_src_attr}]
+----
+include::{sourcedir}/_0230_KthSmallestElementInABst_2.java[tag=answer]
+----
+
+== 参考资料
+
+. https://leetcode.cn/problems/kth-smallest-element-in-a-bst/solutions/1050055/er-cha-sou-suo-shu-zhong-di-kxiao-de-yua-8o07/[230. 二叉搜索树中第K小的元素 - 官方题解^]
+. https://leetcode.cn/problems/kth-smallest-element-in-a-bst/solutions/2361685/230-er-cha-sou-suo-shu-zhong-di-k-xiao-d-n3he/[230. 二叉搜索树中第K小的元素 - 中序遍历，清晰图解^]
+

docs/images/0230-1.png renamed to docs/images/0230-01.png

@@ -277,6 +277,11 @@
 |{doc_base_url}/0912-sort-an-array.adoc[题解]
 |归并，快排都可以
 
+|{counter:codes}
+|{leetcode_base_url}/kth-smallest-element-in-a-bst/[230. Kth Smallest Element in a BST]
+|{doc_base_url}/0230-kth-smallest-element-in-a-bst.adoc[题解]
+|二叉树中根遍历
+
 |===
 
 截止目前，本轮练习一共完成 {codes} 道题。

docs/images/0230-2.png renamed to docs/images/0230-02.png

@@ -0,0 +1,85 @@
+package com.diguage.algo.leetcode;
+
+import com.diguage.algo.util.TreeNode;
+
+/**
+ * = 230. Kth Smallest Element in a BST
+ *
+ * https://leetcode.com/problems/kth-smallest-element-in-a-bst/[Kth Smallest Element in a BST - LeetCode]
+ *
+ * Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.
+ *
+ * Note:
+ * You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
+ *
+ * .Example 1:
+ * [source]
+ * ----
+ * Input: root = [3,1,4,null,2], k = 1
+ *    3
+ *   / \
+ *  1   4
+ *   \
+ *    2
+ * Output: 1
+ * ----
+ *
+ * .Example 2:
+ * [source]
+ * ----
+ * Input: root = [5,3,6,2,4,null,null,1], k = 3
+ *        5
+ *       / \
+ *      3   6
+ *     / \
+ *    2   4
+ *   /
+ *  1
+ * Output: 3
+ * ----
+ *
+ * *Follow up:*
+ *
+ * What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?
+ *
+ * @author D瓜哥 · https://www.diguage.com
+ * @since 2020-01-22 08:27
+ */
+public class _0230_KthSmallestElementInABst_2 {
+  // tag::answer[]
+  /**
+   * Morris 中序遍历
+   *
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2024-07-08 14:51:44
+   */
+  public int kthSmallest(TreeNode root, int k) {
+    TreeNode cur = root;
+    TreeNode mostRight = null;
+    TreeNode result = null;
+    while (cur != null) {
+      mostRight = cur.left;
+      if (mostRight != null) {
+        while (mostRight.right != null && mostRight.right != cur) {
+          mostRight = mostRight.right;
+        }
+        if (mostRight.right == null) {
+          mostRight.right = cur;
+          cur = cur.left;
+          continue;
+        }else {
+          mostRight.right = null;
+        }
+      }
+      k--;
+      if (k == 0) {
+        result = cur;
+        break;
+      }
+      System.out.println(cur.val);
+      cur = cur.right;
+    }
+    return result.val;
+  }
+  // end::answer[]
+}