LeetCode 199. Binary Tree Right Side View

Question

Given the root of 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.

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

Solution

• Solution1 – BFS

class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        if(root == null) return res;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()){
            int size = q.size();
            res.add(q.peek().val);
            for(int i = 0; i < size; i++){
                TreeNode cur = q.poll();
                if(cur.right != null) q.offer(cur.right);
                if(cur.left != null) q.offer(cur.left);
            }
        }
        return res;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)