HIndexII.java

package medium;
/**
 * ClassName: HIndexII.java
 * Author: chenyiAlone
 * Create Time: 2019/5/17 13:47
 * Description: No.275
 * 思路:
 *      1. h 本论文被引用了至少 h 次
 *      2. binary search
 *
 * Given an array of citations sorted in ascending order (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 = [0,1,3,5,6]
 * Output: 3
 * Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them had
 *              received 0, 1, 3, 5, 6 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.
 *
 * Follow up:
 *
 * This is a follow up problem to H-Index, where citations is now guaranteed to be sorted in ascending order.
 * Could you solve it in logarithmic time complexity?
 *
 */
public class HIndexII {
    public int hIndex(int[] citations) {
        int len = citations.length;
        int l = 0, r = len - 1;
        while (l <= r) {
            int mid = (l + r) >> 1;
            if (citations[mid] < len - mid) {
                l = mid + 1;
            } else {
                r = mid - 1;
            }
        }
        return len - l;
    }
}