solve 199.二叉树的右视图

Author: andavid

zh/199.二叉树的右视图.java

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+/*
+ * @lc app=leetcode.cn id=199 lang=java
+ *
+ * [199] 二叉树的右视图
+ *
+ * https://leetcode-cn.com/problems/binary-tree-right-side-view/description/
+ *
+ * algorithms
+ * Medium (63.75%)
+ * Likes:    235
+ * Dislikes: 0
+ * Total Accepted:    47.1K
+ * Total Submissions: 73.9K
+ * Testcase Example:  '[1,2,3,null,5,null,4]'
+ *
+ * 给定一棵二叉树，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。
+ *
+ * 示例:
+ *
+ * 输入: [1,2,3,null,5,null,4]
+ * 输出: [1, 3, 4]
+ * 解释:
+ *
+ * ⁠  1            <---
+ * ⁠/   \
+ * 2     3         <---
+ * ⁠\     \
+ * ⁠ 5     4       <---
+ *
+ *
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+  public List<Integer> rightSideView(TreeNode root) {
+    List<Integer> result = new ArrayList<>();
+    if (root == null) {
+      return result;
+    }
+
+    Queue<TreeNode> queue = new LinkedList<>();
+    queue.offer(root);
+
+    while (!queue.isEmpty()) {
+      int size = queue.size();
+      for (int i = 0; i < size; i++) {
+        TreeNode node = queue.poll();
+        if (node.left != null) {
+          queue.offer(node.left);
+        }
+        if (node.right != null) {
+          queue.offer(node.right);
+        }
+        if (i == size - 1) {
+          result.add(node.val);
+        }
+      }
+    }
+
+    return result;
+  }
+}
+// @lc code=end
+