public static IList <int> PostorderTraversal(LeetCode145TreeNode root)
{
var ans = new List <int>();
var stack = new Stack <LeetCode145TreeNode>();
while (root != null || stack.Count > 0)
{
while (root != null)
{
if (root.right != null)
{
stack.Push(root.right);
}
stack.Push(root);
root = root.left;
}
root = stack.Pop();
if (stack.Count > 0 && root.right == stack.Peek())
{
stack.Pop();
stack.Push(root);
root = root.right;
}
else
{
ans.Add(root.val);
root = null;
}
}
return(ans);
}
public LeetCode145TreeNode(int val = 0, LeetCode145TreeNode left = null, LeetCode145TreeNode right = null)
{
this.val = val;
this.left = left;
this.right = right;
}