func increasingTriplet(nums []int) bool {
	n := len(nums)
	if n < 3 {
		return false
	}
	st := []int{nums[0]}
	top := 0
	for i := 1; top < 2 && i < n; i++ {
		if num := nums[i]; st[top] < num {
			st = append(st, num)
			top++
		} else if num <= st[0] {
			st[0] = num
		} else {
			st[1] = num
		}
	}
	return top == 2
}