package main

func longestConsecutive(nums []int) (max int) {
	exists := make(map[int]bool, len(nums))
	for _, n := range nums {
		exists[n] = true
	}
	done := make(map[int]bool, len(nums))
	for _, n := range nums {
		if _, ok := done[n]; !ok {
			done[n] = true
			l := 1
			for exists[n+1] {
				l++
				n++
				done[n] = true
			}
			n -= l - 1
			for exists[n-1] {
				l++
				n--
				done[n] = true
			}
			if l > max {
				max = l
			}
		}
	}
	return max
}