題目

https://leetcode-cn.com/problems/binary-tree-right-side-view/

題解

本題思路來源于二叉樹的層序遍歷。

• 層序遍歷類似問題：leetcode 637. Average of Levels in Binary Tree
• 如何使用“記錄下一行最右節點”的方式，進行層序遍歷：左神算法：二叉樹的按層打印與ZigZag打印

/*** 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<Integer> rightSideView(TreeNode root) {if (root == null) return new ArrayList<>();ArrayList<Integer> list = new ArrayList<>();LinkedList<TreeNode> queue = new LinkedList<>();queue.add(root);TreeNode curLast = root;TreeNode nextLast = root;while (queue.size() > 0) {TreeNode cur = queue.poll();if (cur.left != null) {nextLast = cur.left;queue.offer(cur.left);}if (cur.right != null) {nextLast = cur.right;queue.offer(cur.right);}if (cur == curLast) { // after this node, goto a new linelist.add(cur.val);curLast = nextLast;}}return list;} }

總結

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