[Leetcode] 199. Binary Tree Right Side View

199. Binary Tree Right Side View

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]
.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        if(root == null) return result;
        List<TreeNode> curLevel = new ArrayList<>();
        curLevel.add(root);
        while(curLevel.size() > 0){
            result.add(curLevel.get(curLevel.size()-1).val);
            List<TreeNode> nxtLevel = new ArrayList<>();
            for(TreeNode cur : curLevel){
                if(cur.left != null) nxtLevel.add(cur.left);
                if(cur.right != null) nxtLevel.add(cur.right);
            }
            curLevel = nxtLevel;
        }
        return result;
    }
}