LeetCode 274. H-Index 二分

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本文介绍了一种计算研究人员h指数的方法。h指数是指一个科学家有h篇论文至少被引用了h次，其余的论文每篇的引用次数不超过h次。通过排序和查找，算法能够有效地确定h指数。

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

According to the definition of h-index on Wikipedia: "A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each."

Example:

Input: citations = [3,0,6,1,5]
Output: 3 
Explanation: [3,0,6,1,5] means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, her h-index is 3.

Note: If there are several possible values for h, the maximum one is taken as the h-index.

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class Solution:
    def hIndex(self, citations: List[int]) -> int:
        citations.sort()
        size = len(citations)

        # idx [0,size-1]
        def f(idx):
            nonlocal citations, size
            return citations[idx] - (size - idx)

        l, r, tgt = 0, size - 1, 0
        while (l <= r):
            mid = l + ((r - l) >> 1)
            fm = f(mid)
            if (tgt > fm):
                l = mid + 1
            else:
                r = mid - 1
        return size-l