flatten-binary-tree-to-linked-list-2.go

// https://leetcode.com/problems/flatten-binary-tree-to-linked-list
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func flatten(root *TreeNode)  {
    ch := make(chan *TreeNode)
    
    go func () {
        preOrderTraverse(root, ch)
        close(ch)
    }()
    
    var prev *TreeNode
    
    for curr := range ch {
        curr.Right = prev
        curr.Left = nil
        prev = curr
    }
}

func preOrderTraverse(root *TreeNode, ch chan *TreeNode) {
    if root == nil {
        return
    }
    
    preOrderTraverse(root.Right, ch)
    preOrderTraverse(root.Left, ch)
    
    ch <- root
}