level travel bst

README.md

@@ -36,7 +36,8 @@
 
 [二叉树的按层遍历相关问题](https://www.cnblogs.com/greyzeng/p/16356829.html)
 - 类似问题一： 二叉树自底向上层序遍历
-
+- 类似问题二：以数组的形式返回每一层节点的平均值
+- 类似问题三：填充每个节点的下一个右侧节点指针
     
 
 ## 更多

src/main/java/git/snippet/leetcode/LeetCode_0116_PopulatingNextRightPointersInEachNode.java → src/main/java/git/snippet/tree/LeetCode_0116_PopulatingNextRightPointersInEachNode.java

-package git.snippet.leetcode;
+package git.snippet.tree;
 
 import java.util.LinkedList;
 import java.util.Queue;
 
-// https://leetcode.cn/problems/populating-next-right-pointers-in-each-node/description/
+// https://leetcode.com/problems/populating-next-right-pointers-in-each-node/description/
 // 本质是树的按层遍历
 // 1. hash表+LinkedList
 // 2. 仅用LinkedList
@@ -16,7 +16,7 @@ import java.util.Queue;
 // 笔记：https://www.cnblogs.com/greyzeng/p/16356829.html
 public class LeetCode_0116_PopulatingNextRightPointersInEachNode {
     // 使用LinkedList作为队列,空间O(N)
-    public static Node connect(Node root) {
+    public Node connect(Node root) {
         if (null == root) {
             return null;
         }
@@ -28,6 +28,7 @@ public class LeetCode_0116_PopulatingNextRightPointersInEachNode {
             size = queue.size();
             // 把每一层用链表串好，pre记录每一层的最后那个位置
             // 用于和下一层的开头连接
+            // 每次把一层搞定
             for (; size > 0; size--) {
                 Node p = queue.poll();
                 if (pre != null) {
@@ -46,7 +47,7 @@ public class LeetCode_0116_PopulatingNextRightPointersInEachNode {
         return root;
     }
 
-    public static Node connect2(Node root) {
+    public Node connect2(Node root) {
         if (root == null) {
             return null;
         }

src/main/java/git/snippet/leetcode/LeetCode_0117_PopulatingNextRightPointersInEachNodeII.java → src/main/java/git/snippet/tree/LeetCode_0117_PopulatingNextRightPointersInEachNodeII.java

-package git.snippet.leetcode;
+package git.snippet.tree;
 
 // 和116题一样
-// https://leetcode.cn/problems/populating-next-right-pointers-in-each-node-ii/
+// https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/
 // 笔记：https://www.cnblogs.com/greyzeng/p/16356829.html
 public class LeetCode_0117_PopulatingNextRightPointersInEachNodeII {
-    public static Node connect(Node root) {
+    // 采用自定义队列
+    public Node connect(Node root) {
         if (root == null) {
             return null;
         }
@@ -33,7 +34,7 @@ public class LeetCode_0117_PopulatingNextRightPointersInEachNodeII {
         return root;
     }
 
-    public static class Node {
+    public class Node {
         public int val;
         public Node left;
         public Node right;

src/main/java/git/snippet/leetcode/LeetCode_0637_AverageOfLevelsInBinaryTree.java → src/main/java/git/snippet/tree/LeetCode_0637_AverageOfLevelsInBinaryTree.java

-/*
- * Given a non-empty binary tree, return the average value of the nodes on each level in the form of
- * an array. Example 1: Input: 3 / \ 9 20 / \ 15 7 Output: [3, 14.5, 11] Explanation: The average
- * value of nodes on level 0 is 3, on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5,
- * 11].
- */
-package git.snippet.leetcode;
+package git.snippet.tree;
 
 import java.util.ArrayList;
 import java.util.LinkedList;
@@ -12,10 +6,10 @@ import java.util.List;
 import java.util.Queue;
 
 // 笔记：https://www.cnblogs.com/greyzeng/p/16356829.html
-// https://leetcode.cn/problems/average-of-levels-in-binary-tree/description/
+// https://leetcode.com/problems/average-of-levels-in-binary-tree/description/
 // 按层遍历，然后求每层的平均值
 public class LeetCode_0637_AverageOfLevelsInBinaryTree {
-    public static List<Double> averageOfLevels(TreeNode root) {
+    public List<Double> averageOfLevels(TreeNode root) {
         if (null == root) {
             return new ArrayList<>();
         }
@@ -23,33 +17,32 @@ public class LeetCode_0637_AverageOfLevelsInBinaryTree {
         Queue<TreeNode> queue = new LinkedList<>();
         TreeNode curEnd = root;
         TreeNode nextEnd = null;
-        int numOfNodes = 0;
-        Double sumOfNodesVal = 0d;
+        int numOfNodes = 0; // 记录每一层的节点个数
+        double sumOfNodesVal = 0d; // 记录每一层的节点平均值（累计值除以个数）
         queue.offer(root);
         while (!queue.isEmpty()) {
-            TreeNode poll = queue.poll();
-            if (null != poll.left) {
-                queue.offer(poll.left);
-                nextEnd = poll.left;
+            TreeNode cur = queue.poll();
+            if (null != cur.left) {
+                queue.offer(cur.left);
+                nextEnd = cur.left;
             }
-            if (null != poll.right) {
-                queue.offer(poll.right);
-                nextEnd = poll.right;
+            if (null != cur.right) {
+                queue.offer(cur.right);
+                nextEnd = cur.right;
             }
             numOfNodes++;
-            sumOfNodesVal += poll.val;
-            if (poll == curEnd) {
+            sumOfNodesVal += cur.val;
+            if (cur == curEnd) {
                 result.add(sumOfNodesVal / numOfNodes);
                 sumOfNodesVal = 0d;
                 numOfNodes = 0;
                 curEnd = nextEnd;
             }
         }
-
         return result;
     }
 
-    public static class TreeNode {
+    public class TreeNode {
         int val;
         TreeNode left;
         TreeNode right;