package LeetCode;

import javafx.util.Pair;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

public class LeetCode102 {

    /// 102. Binary Tree Level Order Traversal
    /// https://leetcode.com/problems/binary-tree-level-order-traversal/description/
    /// 
    /// : O(n), n
    /// : O(n)

    // Definition for a binary tree node.
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }

    public List levelOrder(TreeNode root) {

        ArrayList res = new ArrayList();
        if(root == null)
            return res;

        // LinkedList
        LinkedList queue = new LinkedList();

        queue.addLast(new Pair(root, 0));
        while(!queue.isEmpty()){

            // TreeNodelevel
            Pair front = queue.removeFirst();
            TreeNode node = front.getKey();
            int level = front.getValue();

            // level == res.size() --->--->new ArrayList()
            if(level == res.size()) {
                res.add(new ArrayList());
            }
            assert level < res.size();

            res.get(level).add(node.val);
            if(node.left != null)
                queue.addLast(new Pair(node.left, level + 1));
            if(node.right != null)
                queue.addLast(new Pair(node.right, level + 1));
        }

        return res;
    }
}