public Node(int _val, Node _left, Node _right, Node _next)
{
val = _val;
left = _left;
right = _right;
next = _next;
}
/// <summary>
/// BFS 层次遍历法
/// </summary>
/// <param name="root"></param>
/// <returns></returns>
public Node Connect_V1(Node root)
{
if (root == null)
{
return(null);
}
Queue <Node> queue = new Queue <Node>();
queue.Enqueue(root);
while (queue.Count > 0)
{
var size = queue.Count;
while (size-- > 0)
{
var node = queue.Dequeue();
if (size > 0)
{
node.next = queue.Peek();
}
if (node.left != null)
{
queue.Enqueue(node.left);
}
if (node.right != null)
{
queue.Enqueue(node.right);
}
}
}
return(root);
}
/// <summary>
/// 层次遍历
/// </summary>
/// <param name="root"></param>
/// <returns></returns>
public Node Connect_V1(Node root)
{
if (root == null)
{
return(null);
}
Queue <Node> stack = new Queue <Node>();
stack.Enqueue(root);
while (stack.Count > 0)
{
Node pre = null;
var count = stack.Count;
while (count-- > 0)
{
var node = stack.Dequeue();
if (count > 0)
{
node.next = stack.Peek();
}
if (node.left != null)
{
stack.Enqueue(node.left);
}
if (node.right != null)
{
stack.Enqueue(node.right);
}
}
}
return(root);
}
public void test_V1()
{
var node = new Node(1,
new Node(2, new Node(4), new Node(5)),
new Node(3, new Node(6), new Node(7)));
var res = target.Connect_V1(node);
Assert.True(res.left.next == res.right);
}
private Node nextNode(Node node)
{
while (node != null)
{
if (node.left != null)
{
return(node.left);
}
if (node.right != null)
{
return(node.right);
}
node = node.next;
}
return(null);
}
/// <summary>
/// BFS 层次遍历法
/// </summary>
/// <param name="root"></param>
/// <returns></returns>
public Node Connect(Node root)
{
if (root == null)
{
return(null);
}
Queue <Node> stack = new Queue <Node>();
stack.Enqueue(root);
while (stack.Count > 0)
{
var index = stack.Count;
var rightNode = stack.Dequeue();
if (rightNode.right != null)
{
stack.Enqueue(rightNode.right);
}
if (rightNode.left != null)
{
stack.Enqueue(rightNode.left);
}
while (index-- > 0)
{
var node = stack.Dequeue();
node.next = rightNode;
rightNode = node;
if (node.right != null)
{
stack.Enqueue(node.right);
}
if (node.left != null)
{
stack.Enqueue(node.left);
}
}
}
return(root);
}
public Node connect_V4(Node root)
{
if (root == null)
{
return(root);
}
//cur我们可以把它看做是每一层的链表
Node cur = root;
while (cur != null)
{
//遍历当前层的时候，为了方便操作在下一
//层前面添加一个哑结点（注意这里是访问
//当前层的节点，然后把下一层的节点串起来）
Node dummy = new Node(0);
//pre表示访下一层节点的前一个节点
Node pre = dummy;
//然后开始遍历当前层的链表
while (cur != null)
{
if (cur.left != null)
{
//如果当前节点的左子节点不为空，就让pre节点
//的next指向他，也就是把它串起来
pre.next = cur.left;
//然后再更新pre
pre = pre.next;
}
//同理参照左子树
if (cur.right != null)
{
pre.next = cur.right;
pre = pre.next;
}
//继续访问这一行的下一个节点
cur = cur.next;
}
//把下一层串联成一个链表之后，让他赋值给cur，
//后续继续循环，直到cur为空为止
cur = dummy.next;
}
return(root);
}
public Node Connect_V3(Node root)
{
if (root == null)
{
return(null);
}
if (root.left != null)
{
if (root.right != null)
{
// 若右子树不为空，则左子树的 next 即为右子树
root.left.next = root.right;
}
else
{
// 若右子树为空，则右子树的 next 由根节点的 next 得出
root.left.next = nextNode(root.next);
}
}
if (root.right != null)
{
// 右子树的 next 由根节点的 next 得出
root.right.next = nextNode(root.next);
}
// 先确保 root.right 下的节点的已完全连接，因 root.left 下的节点的连接
// 需要 root.left.next 下的节点的信息，若 root.right 下的节点未完全连
// 接（即先对 root.left 递归），则 root.left.next 下的信息链不完整，将
// 返回错误的信息。可能出现的错误情况如下图所示。此时，底层最左边节点将无
// 法获得正确的 next 信息：
// o root
// / \
// root.left o —— o root.right
// / / \
// o —— o o
// / / \
// o o o
Connect_V3(root.right);
Connect_V3(root.left);
return(root);
}
/// <summary>
/// 层次遍历
/// </summary>
/// <param name="root"></param>
/// <returns></returns>
public Node Connect(Node root)
{
if (root == null)
{
return(null);
}
Stack <Node> stack = new Stack <Node>();
stack.Push(root);
while (stack.Count > 0)
{
List <Node> florList = new List <Node>();
while (stack.Count > 0)
{
var node = stack.Pop();
if (node.left != null)
{
florList.Add(node.left);
}
if (node.right != null)
{
florList.Add(node.right);
}
}
for (int i = 0; i < florList.Count; i++)
{
if (i + 1 < florList.Count)
{
florList[i].next = florList[i + 1];
}
stack.Push(florList[florList.Count - i - 1]);
}
}
return(root);
}
