1305-AllElementsInTwoBinarySearchTrees.cs

//-----------------------------------------------------------------------------
// Runtime: 360ms
// Memory Usage: 49.2 MB
// Link: https://leetcode.com/submissions/detail/391562509/
//-----------------------------------------------------------------------------

using System.Collections.Generic;

namespace LeetCode
{
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     public int val;
     *     public TreeNode left;
     *     public TreeNode right;
     *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
    public class _1305_AllElementsInTwoBinarySearchTrees
    {
        public IList<int> GetAllElements(TreeNode root1, TreeNode root2)
        {
            var stack1 = new Stack<TreeNode>();
            var stack2 = new Stack<TreeNode>();

            var result = new List<int>();
            while (root1 != null || root2 != null || stack1.Count > 0 || stack2.Count > 0)
            {
                while (root1 != null)
                {
                    stack1.Push(root1);
                    root1 = root1.left;
                }
                while (root2 != null)
                {
                    stack2.Push(root2);
                    root2 = root2.left;
                }

                if ((stack2.Count == 0 && stack1.Count > 0) || (stack2.Count > 0 && stack1.Count > 0 && stack1.Peek().val <= stack2.Peek().val))
                {
                    root1 = stack1.Pop();
                    result.Add(root1.val);
                    root1 = root1.right;
                }
                else if ((stack1.Count == 0 && stack2.Count > 0) || (stack1.Count > 0 && stack2.Count > 0 && stack1.Peek().val >= stack2.Peek().val))
                {
                    root2 = stack2.Pop();
                    result.Add(root2.val);
                    root2 = root2.right;
                }
            }

            return result;
        }
    }
}