【LeetCode】Binary Tree Right Side View 解題報告，leetcodebinary

【LeetCode】Binary Tree Right Side View 解題報告，leetcodebinary

【題目】

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <--- /   \2     3         <--- \     \  5     4       <---

You should return [1, 3, 4].

【解析】

題意：給定一棵二叉樹，返回從右邊看這棵二叉樹所看到的節點序列（從上到下）。

思路：層次遍曆法。遍曆到每層最後一個節點時，把其放到結果集中。

【Java代碼】

public class Solution {    public List<Integer> rightSideView(TreeNode root) {        List<Integer> ans = new ArrayList<Integer>();        if (root == null) return ans;                LinkedList<TreeNode> queue = new LinkedList<TreeNode>();        queue.add(root);        queue.add(null);                while (!queue.isEmpty()) {            TreeNode node = queue.pollFirst();                        if (node == null) {                if (queue.isEmpty()) {                    break;                } else {                    queue.add(null);                }            } else {                // add the rightest to the answer                if (queue.peek() == null) {                    ans.add(node.val);                }                                if (node.left != null) {                    queue.add(node.left);                }                if (node.right != null) {                    queue.add(node.right);                }            }        }                return ans;    }}