go union find

source

func merge(a int, b int) {
	a = find(a)
	b = find(b)
	if a == b {
		return
	}
	root[b] = a
}

func find(n int) int {
	if root[n] < 0 {
		return n
	}
	root[n] = find(root[n])
	return root[n]
}