Binary Tree Right Side View

In BFS, process each level with its saved queue length and append the value of the final node removed from that level. Since children are enqueued left then right, that final node is the visible rightmost node at the depth. Alternatively, use DFS that visits right before left and maintain result[depth] only if it is not set; the first node reached at a depth is then the right-side view. Both are correct, but explain the ordering property rather than merely choosing one. Do not use a single root-to-leaf path, because the right-side node can come from a different branch at different depths. Test null, a left-only chain where every node is visible, a right-only chain, and a tree where a deep left child appears after a shallow right branch. Time is O(n). BFS uses O(w) queue space, while recursive DFS uses O(h) stack space.