Binary Tree Vertical Order Traversal
LeetCode 314 • Medium • Trees
Input: root = [3,9,20,null,null,15,7] → Output: [[9],[3,15],[20],[7]]
BFS queue of (node, col); map col→vals; return columns sorted left→right.
TimeO(n log n)BFS + sort cols
SpaceO(n)queue + map
Queue: []Cols: {}
Current node
In queue
Column highlight
Processed
Queue
empty
col_map
{}
Ready
Press Play. BFS with column index: left col−1, right col+1.