[LeetCode] 199. Binary Tree Right Side View

linspiration

Problem

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.

Example:

``````Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

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

``````

Solution - BFS

``````class Solution {
public List<Integer> rightSideView(TreeNode root) {
//save into stack in level order
List<Integer> res = new ArrayList<>();
if (root == null) return res;
Deque<TreeNode> queue = new ArrayDeque<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode cur = queue.poll();
if (cur.left != null) queue.offer(cur.left);
if (cur.right != null) queue.offer(cur.right);
}
}
return res;
}
}``````

Solution - DFS

``````class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> res = new ArrayList<>();
if (root == null) return res;
dfs(root, 0, res);
return res;
}
private void dfs(TreeNode root, int level, List<Integer> res) {
if (root == null) return;