Solution3.go

func hIndex(citations []int) int {
	l, r := 0, len(citations)
	for l < r {
		mid := (l + r + 1) >> 1
		s := 0
		for _, x := range citations {
			if x >= mid {
				s++
			}
		}
		if s >= mid {
			l = mid
		} else {
			r = mid - 1
		}
	}
	return l
}