116.Populating Next Right Pointers in Each Node.go

package leetcode

type Node struct {
	Val   int
	Left  *Node
	Right *Node
	Next  *Node
}

// 解法一：迭代
func connect(root *Node) *Node {
	if root == nil {
		return root
	}
	q := []*Node{root}
	for len(q) > 0 {
		var p []*Node
		// 遍历这一层的所有节点
		for i, node := range q {
			if i+1 < len(q) {
				node.Next = q[i+1]
			}
			if node.Left != nil {
				p = append(p, node.Left)
			}
			if node.Right != nil {
				p = append(p, node.Right)
			}
		}
		q = p
	}
	return root
}

// 解法二 递归
func connect2(root *Node) *Node {
	if root == nil {
		return nil
	}
	connectTwoNode(root.Left, root.Right)
	return root
}

func connectTwoNode(node1, node2 *Node) {
	if node1 == nil || node2 == nil {
		return
	}
	node1.Next = node2
	connectTwoNode(node1.Left, node1.Right)
	connectTwoNode(node2.Left, node2.Right)
	connectTwoNode(node1.Right, node2.Left)
}