/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List> verticalOrder(TreeNode root) {
List> result = new ArrayList<>();
if(root == null) return result;
Map> map = new HashMap<>();
Queue q = new LinkedList<>();
Queue cols = new LinkedList<>();
q.add(root);
cols.add(0);
int min=0, max=0;
while(!q.isEmpty())
{
TreeNode node = q.poll();
int col = cols.poll();
if(!map.containsKey(col))
map.put(col, new ArrayList());
map.get(col).add(node.val);
if(node.left != null)
{
q.add(node.left);
cols.add(col-1);
min = Math.min(min, col-1);
}
if(node.right != null)
{
q.add(node.right);
cols.add(col+1);
max = Math.max(max, col+1);
}
}
for(int i=min; i<=max; i++)
result.add(map.get(i));
return result;
}
}