LeetCode-H Index II

Algorithm record

LeetCode topic:

  You are given an integer array citations, where citations[i] represents the number of times the researcher's ith paper has been cited, citations has been sorted in ascending order. Calculates and returns the researcher's h-index.

  Please design and implement an algorithm with logarithmic time complexity to solve this problem.

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illustrate

1. The topic

输入：citations = [3,0,6,1,5]
输出：3 
解释：给定数组表示研究者总共有 5 篇论文，每篇论文相应的被引用了 3, 0, 6, 1, 5 次。
     由于研究者有 3 篇论文每篇至少被引用了 3 次，其余两篇论文每篇被引用不多于 3 次，所以她的 h 指数是 3。
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2. Analysis

• This question is the same as the H index , but requires a lognlevel .
• And when you think of this level of query calculation, it must be a two-point play. Before, we increased it through a step-by-step traversal from the front to the back, and you can cut half of it with one two-point.

class Solution {
    public int hIndex(int[] citations) {
        int n = citations.length;
        int left = 0, right = n - 1;
        while (left <= right) {
            int mid = (right + left) / 2;
            if (citations[mid] >= n - mid) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return n - left;
    }
}
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Summarize

Binary search.