314. Binary Tree Vertical Order Traversal

314. Binary Tree Vertical Order Traversal

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

 

 

use two stacks 

314. Binary Tree Vertical Order Traversal


class Solution {
    public List<List<Integer>> verticalOrder(TreeNode root) {
      HashMap<Integer, List<Integer>> map = new HashMap<>();
      List<List<Integer>> result = new ArrayList<>();
      Queue<TreeNode> queue = new LinkedList<>();
      Queue<Integer> cols = new LinkedList<>();
      
      if(root == null){
        return result;
      }
      
      int max = 0;
      int min = 0;
      
      queue.offer(root);
      cols.offer(0);
      while(!queue.isEmpty()){
        TreeNode cur = queue.poll();
        int col = cols.poll();
        if(!map.containsKey(col)){
          map.put(col, new ArrayList<Integer>());
        }
        map.get(col).add(cur.val);
        
        if(cur.left != null){
          queue.offer(cur.left);
          cols.offer(col - 1);
          min = Math.min(min, col - 1);
        }
        
        if(cur.right != null){
          queue.offer(cur.right);
          cols.offer(col + 1);
          max = Math.max(max, col + 1);
        }
      }
      
      for(int i = min; i <= max; i++){
        List<Integer> current_col = map.get(i);
        result.add(current_col);
      }
      return result;
    }
}