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leetcode314.java
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leetcode314.java
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
/*
Time: O(n). one-pass
Space: O(n). size of map is n.
*/
public class Solution {
public List<List<Integer>> verticalOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if(root == null)
return res;
Map<Integer, ArrayList<Integer>> map = new HashMap<>();
Queue<TreeNode> q = new LinkedList<>();
Queue<Integer> 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<Integer>());
map.get(col).add(node.val);
if(node.left != null){
q.add(node.left);
cols.add(col - 1);
if(col <= min)
min = col - 1;
}
if(node.right != null){
q.add(node.right);
cols.add(col + 1);
if(col >= max)
max = col + 1;
}
}
for(int i = min; i <= max; i++){
res.add(map.get(i));
}
return res;
}
}