BinaryTreeRightSideView.java

package com.leetcode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class BinaryTreeRightSideView {
    //https://leetcode.com/problems/binary-tree-right-side-view/
    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.size() > 0){
                int size = queue.size();
                while(size > 0){
                    TreeNode node = queue.poll();
                    size--;
                    if(size == 0)
                        result.add(node.val);
                    if(node.left != null) queue.offer(node.left);
                    if(node.right != null) queue.offer(node.right);
                }
            }

            return result;
        }
    }

    //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;
        }
    }
}