You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 1110.go
    path of file: ./repos/Leetcode/src/1110-Delete-Nodes-And-Return-Forest
    
    the code of the file until where you have to start completion: var res []*TreeNode
var delete_set map[int]bool

func delNode
    
func delNodes(root *TreeNode, to_delete []int) []*TreeNode {
    delete_set = make(map[int]bool)
    for _, v := range to_delete {
        delete_set[v] = true
    }
    
    res = []*TreeNode{}
    preOrder(root, true)
    return res
}