func majorityElement(nums []int) (ans []int) {
	n1, n2, c1, c2 := 0, 0, 0, 0
	for _, n := range nums { // At most 2 majority elements occur more than n/3 times.
	// Use two counters to vote the occurence of the numbers.
		switch {
		case n == n1:
			c1++
		case n == n2:
			c2++
		case c1 == 0:
			n1, c1 = n, 1
		case c2 == 0:
			n2, c2 = n, 1
		default:
			c1, c2 = c1-1, c2-1
		}
	}
	c1, c2 = 0, 0
	for _, n := range nums {
		switch n {
		case n1:
			c1++
		case n2:
			c2++
		}
	}
	if len(nums)/3 < c1 {
		ans = append(ans, n1)
	}
	if len(nums)/3 < c2 {
		ans = append(ans, n2)
	}
	return
}