102:二叉树的层序遍历

src/main/java/leetcode/editor/cn/BinaryTreeLevelOrderTraversal.java

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+//给你一个二叉树，请你返回其按 层序遍历 得到的节点值。 （即逐层地，从左到右访问所有节点）。 
+//
+// 
+//
+// 示例： 
+//二叉树：[3,9,20,null,null,15,7], 
+//
+// 
+//    3
+//   / \
+//  9  20
+//    /  \
+//   15   7
+// 
+//
+// 返回其层序遍历结果： 
+//
+// 
+//[
+//  [3],
+//  [9,20],
+//  [15,7]
+//]
+// 
+// Related Topics 树 广度优先搜索 二叉树 
+// 👍 945 👎 0
+
+package leetcode.editor.cn;
+
+import com.code.leet.entiy.TreeNode;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+//102:二叉树的层序遍历
+public class BinaryTreeLevelOrderTraversal {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new BinaryTreeLevelOrderTraversal().new Solution();
+    }
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+
+    /**
+     * 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 {
+        public List<List<Integer>> levelOrder(TreeNode root) {
+            if (root == null) {
+                return new ArrayList<>();
+            }
+            Queue<TreeNode> queue = new LinkedList<>();
+            List<List<Integer>> result = new ArrayList<>();
+            queue.add(root);
+            while (!queue.isEmpty()) {
+                int size = queue.size();
+                List<Integer> list = new ArrayList<>();
+                for (int i = 0; i < size; i++) {
+                    TreeNode temp = queue.poll();
+                    list.add(temp.val);
+                    if (temp.left != null) {
+                        queue.add(temp.left);
+                    }
+                    if (temp.right != null) {
+                        queue.add(temp.right);
+                    }
+                }
+                result.add(list);
+            }
+            return result;
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

src/main/java/leetcode/editor/cn/BinaryTreeLevelOrderTraversal.md

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+<p>给你一个二叉树，请你返回其按 <strong>层序遍历</strong> 得到的节点值。 （即逐层地，从左到右访问所有节点）。</p>
+
+<p> </p>
+
+<p><strong>示例：</strong><br />
+二叉树：<code>[3,9,20,null,null,15,7]</code>,</p>
+
+<pre>
+    3
+   / \
+  9  20
+    /  \
+   15   7
+</pre>
+
+<p>返回其层序遍历结果：</p>
+
+<pre>
+[
+  [3],
+  [9,20],
+  [15,7]
+]
+</pre>
+<div><div>Related Topics</div><div><li>树</li><li>广度优先搜索</li><li>二叉树</li></div></div>\n<div><li>👍 945</li><li>👎 0</li></div>