//dfs解法
public IList <IList <int> > LevelOrderBottom01(TreeNode root)
{
List <IList <int> > res = new List <IList <int> >();
if (root == null)
{
return(res);
}
Stack <TreeNodeVO> stack = new Stack <TreeNodeVO>();
stack.Push(new TreeNodeVO(root, 0));
while (stack.Count > 0)
{
TreeNodeVO vo = stack.Pop();
if (vo.node != null)
{
if (res.Count < vo.lv + 1)
{
res.Insert(0, new List <int>());
}
int idx = res.Count - (vo.lv + 1);
stack.Push(new TreeNodeVO(vo.node.right, vo.lv + 1));
stack.Push(new TreeNodeVO(vo.node.left, vo.lv + 1));
res[idx].Add(vo.node.val);
}
}
return(res);
}
//bfs解法
public IList <IList <int> > LevelOrderBottom02(TreeNode root)
{
List <IList <int> > res = new List <IList <int> >();
if (root == null)
{
return(res);
}
Queue <TreeNodeVO> queue = new Queue <TreeNodeVO>();
queue.Enqueue(new TreeNodeVO(root, 0));
while (queue.Count > 0)
{
int lvNum = queue.Count;
List <int> cur = new List <int>();
for (int i = 0; i < lvNum; i++)
{
TreeNodeVO vo = queue.Dequeue();
if (vo.node.left != null)
{
queue.Enqueue(new TreeNodeVO(vo.node.left, vo.lv + 1));
}
if (vo.node.right != null)
{
queue.Enqueue(new TreeNodeVO(vo.node.right, vo.lv + 1));
}
cur.Add(vo.node.val);
}
res.Insert(0, cur);
}
return(res);
}
