四刷102

Author: diguage

docs/0102-binary-tree-level-order-traversal.adoc

@@ -1,18 +1,11 @@
 [#0102-binary-tree-level-order-traversal]
-= 102. Binary Tree Level Order Traversal
+= 102. 二叉树的层序遍历
 
-{leetcode}/problems/binary-tree-level-order-traversal/[LeetCode - Binary Tree Level Order Traversal^]
+https://leetcode.cn/problems/binary-tree-level-order-traversal/[LeetCode - 102. 二叉树的层序遍历 ^]
 
-这个题其实很简单，只要保持需要读取值的那一层的节点就可以了。
-
-Given a binary tree, return the _level order_ traversal of its nodes' values. (ie, from left to right, level by level).
-
-
-For example:
-
-
-Given binary tree `[3,9,20,null,null,15,7]`,
+给你二叉树的根节点 `root` ，返回其节点值的 *层序遍历* 。（即逐层地，从左到右访问所有节点）。
 
+*示例 1：*
 
 [subs="verbatim,quotes,macros"]
 ----
@@ -23,21 +16,34 @@ Given binary tree `[3,9,20,null,null,15,7]`,
    15   7
 ----
 
+....
+输入：root = [3,9,20,null,null,15,7]
+输出：[[3],[9,20],[15,7]]
+....
 
-return its level order traversal as:
+*示例 2：*
 
+....
+输入：root = [1]
+输出：[[1]]
+....
 
-[subs="verbatim,quotes,macros"]
-----
-[
-  [3],
-  [9,20],
-  [15,7]
-]
-----
+*示例 3：*
+
+....
+输入：root = []
+输出：[]
+....
+
+*提示：*
+
+* 树中节点数目在范围 `[0, 2000]` 内
+* `+-1000 <= Node.val <= 1000+`
 
 == 思路分析
 
+这个题其实很简单，只要保持需要读取值的那一层的节点就可以了。
+
 image:images/0102-00.png[]
 
 [[src-0102]]
@@ -69,6 +75,15 @@ include::{sourcedir}/_0102_BinaryTreeLevelOrderTraversal_2.java[tag=answer]
 include::{sourcedir}/_0102_BinaryTreeLevelOrderTraversal_3.java[tag=answer]
 ----
 --
+
+三刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0102_BinaryTreeLevelOrderTraversal_4.java[tag=answer]
+----
+--
 ====
 
 TIP: TODO：还可以优化成只用一个队列对象，思考如何实现？

logbook/202503.adoc

@@ -90,6 +90,11 @@ endif::[]
 |{doc_base_url}/0023-merge-k-sorted-lists.adoc[题解]
 |✅ 多路归并
 
+|{counter:codes2503}
+|{leetcode_base_url}/binary-tree-level-order-traversal/[102. Binary Tree Level Order Traversal^]
+|{doc_base_url}/0102-binary-tree-level-order-traversal.adoc[题解]
+|✅ 广度优先搜索
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

src/main/java/com/diguage/algo/leetcode/_0102_BinaryTreeLevelOrderTraversal_4.java

@@ -0,0 +1,38 @@
+package com.diguage.algo.leetcode;
+
+import com.diguage.algo.util.TreeNode;
+
+import java.util.*;
+
+public class _0102_BinaryTreeLevelOrderTraversal_4 {
+  // tag::answer[]
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-03-31 07:31:39
+   */
+  public List<List<Integer>> levelOrder(TreeNode root) {
+    if (root == null) {
+      return Collections.emptyList();
+    }
+    List<List<Integer>> result = new LinkedList<>();
+    Queue<TreeNode> queue = new LinkedList<>();
+    queue.offer(root);
+    while (!queue.isEmpty()) {
+      int size = queue.size();
+      List<Integer> level = new ArrayList<>(size);
+      for (int i = 0; i < size; i++) {
+        TreeNode node = queue.poll();
+        level.add(node.val);
+        if (node.left != null) {
+          queue.offer(node.left);
+        }
+        if (node.right != null) {
+          queue.offer(node.right);
+        }
+      }
+      result.add(level);
+    }
+    return result;
+  }
+  // end::answer[]
+}