public static string Serialize(LeetCode449TreeNode root)
{
var sb = PostOrderTraversal(root, new StringBuilder());
// remove the extra trailer delimiter
if (sb.Length > 0)
{
sb.Remove(sb.Length - 1, 1);
}
return(sb.ToString());
}
private static StringBuilder PostOrderTraversal(LeetCode449TreeNode root, StringBuilder sb)
{
if (root == null)
{
return(sb);
}
PostOrderTraversal(root.left, sb);
PostOrderTraversal(root.right, sb);
sb.Append(root.val);
sb.Append(' ');
return(sb);
}
private static LeetCode449TreeNode BuildTree(int lower, int upper, IList <int> nums)
{
if (nums.Count == 0)
{
return(null);
}
var val = nums[nums.Count - 1];
// make sure this matches the BST definition
if (val < lower || val > upper)
{
return(null);
}
// keep processing from the end of list
nums.RemoveAt(nums.Count - 1);
var root = new LeetCode449TreeNode(val);
root.right = BuildTree(val, upper, nums);
root.left = BuildTree(lower, val, nums);
return(root);
}