https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/

populating-next-right-pointers-in-each-node-ii.go

/**
 * Definition for a Node.
 * type Node struct {
 *     Val int
 *     Left *Node
 *     Right *Node
 *     Next *Node
 * }
 */

type LevelNode struct {
    node *Node
    level int
}

func connect(root *Node) *Node {
    if root == nil {
        return nil
    }
    
    queue := []*LevelNode{{
        node: root,
        level: 0,
    }}
    
    var prev *LevelNode
    
    for len(queue) > 0 {
        item := queue[0]
        queue = queue[1:]
        
        if item.node.Left != nil {
            queue = append(queue, &LevelNode{
                node: item.node.Left,
                level: item.level + 1,
            })
        }
        
        if item.node.Right != nil {
            queue = append(queue, &LevelNode{
                node: item.node.Right,
                level: item.level + 1,
            })
        }
        
        if prev != nil && prev.level == item.level {
            prev.node.Next = item.node
        }
        
        prev = item
    }
    
    return root
}