# (specail) 314. Binary Tree Vertical Order Traversal

```
T: O(n)
S: O(n)
```

```java
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<List<Integer>> verticalOrder(TreeNode root) {
        List<List<Integer>> result = new ArrayList<>();
        if (root == null) {
            return result;
        }
        Map<Integer, List<Integer>> map = new HashMap<>();
        Queue<TreeNode> queue = new LinkedList<>();
        Queue<Integer> colQueue = new LinkedList<>();
        queue.offer(root);
        colQueue.offer(0);

        // for range!
        int min = Integer.MAX_VALUE;
        int max = Integer.MIN_VALUE;
        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            
            int col = colQueue.poll();
            map.computeIfAbsent(col, k -> new ArrayList<>()).add(cur.val);
            min = Math.min(min, col);
            max = Math.max(max, col);
            
            if (cur.left != null) {
                queue.offer(cur.left);
                colQueue.offer(col-1);
            }
            if (cur.right != null) {
                queue.offer(cur.right);
                colQueue.offer(col+1);
            }
        }
        for (int i = min; i <= max; i++) {
            result.add(map.get(i));
        }
        return result;
    }
}


/**
use another queue -> left put col - 1
right put col+1

T: O(n)
S: O(n)
 */
```
