題目：199. Binary Tree Right Side View

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

• 等級：Medium

class Solution {
    private int maxlevel = 0;
    public void right(TreeNode root,int level,List<Integer> save)
    {
        if (root == null)
            return;
        if (maxlevel < level)
        {
            save.add(root.val);
            maxlevel = level;
        }
        right(root.right,level+1,save);
        right(root.left,level+1,save);
    }
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> save = new ArrayList<Integer>();
        right(root,1,save);
        return save;
    }
}

• Time complexity: O(n)
• Space complexity: O(n)

題目：116. Populating Next Right Pointers in Each Node

連結：https://leetcode.com/problems/populating-next-right-pointers-in-each-node/

• 等級：Medium

class Solution {
    public Node connect(Node root) {
        Node head = root;
        for(; root != null; root = root.left) 
            for(Node cur = root; cur != null; cur = cur.next) 
                if(cur.left != null) {
                    cur.left.next = cur.right;
                    if(cur.next != null) cur.right.next = cur.next.left;
                } else break;
        
        return head;
    }
}

• Time complexity: O(n)
• Space complexity: O(1)