Leetcode 582

Both of these solutions operate on the same idea:

We add all the parents and children to a map in the format of map[parent] []children (map of a parent then an array of children)
Then we add the kill value to the result and the kills children (From the map), and then the kill’s children’s children, and so on (kill, kill children, kills children's children).

Iterative

If you don’t understand stack = append(stack, m[pop]...), it is basically doing:

for _, i := range m[pop] {
    stack = append(stack, i)
}

func killProcess(pid []int, ppid []int, kill int) []int {
	res := []int{}
    stack := []int{kill}
    m := make(map[int] []int )
	
    for i := 0; i < len(pid); i++ {
        m[ppid[i]] = append(m[ppid[i]], pid[i])
    }
    
    for len(stack) != 0 {
        pop := stack[len(stack) - 1]
        stack = stack[:len(stack) - 1]
        res = append(res, pop)
        stack = append(stack, m[pop]...)
    }
    
	return res
}

Recursive

func killProcess(pid []int, ppid []int, kill int) []int {
    m := make(map[int] []int )
	
    for i := 0; i < len(pid); i++ {
        m[ppid[i]] = append(m[ppid[i]], pid[i])
    }
    
    return helper(kill, m, []int{})
}

func helper(kill int, m map[int] []int, res []int) []int {
    res = append(res, kill)
    
    for _, n := range m[kill] {
        res = helper(n, m, res)
    }
    
    return res
}