[프로그래머스] Lv 2. H-index

def solution(citations):
    num_paper = len(citations)
    #citation.sort(reverse=True)
    
    def quick_sort_reverse(citations):
        if len(citations) <= 1:
            return citations
        else:
            pivot = citations[0]
            greater = [x for x in citations[1:] if x > pivot]
            lesser = [x for x in citations[1:] if x <= pivot]
            return quick_sort_reverse(greater) + [pivot] + quick_sort_reverse(lesser)
    
    sorted = quick_sort_reverse(citations)
    for i in range(num_paper-1, -1,-1):
        if i+1 <= sorted[i]:
            return i+1
    answer = 0
    return answer