feat: 2025-10-28打卡

230.kth-smallest-element-in-a-bst.java

@@ -0,0 +1,58 @@
+/*
+ * @lc app=leetcode id=230 lang=java
+ *
+ * [230] Kth Smallest Element in a BST
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+
+    static class State{
+        int result;
+        int order;
+        int targetOrder;
+        boolean found;
+    }
+
+    public int kthSmallest(TreeNode root, int k) {
+        State st = new State();
+        st.found = false;
+        st.targetOrder = k;
+        st.order = 0;
+        travel(root, st);
+        return st.result;
+    }
+
+    private void travel(TreeNode node, State st) {
+        if(node == null) {
+            return;
+        }
+        travel(node.left, st);
+        st.order++;
+        if(st.found) {
+            return;
+        } else if(st.order == st.targetOrder) {
+            st.result = node.val;
+            st.found = true;
+        } else {
+            travel(node.right, st);
+        }
+    }
+}
+// @lc code=end
+