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g0201_0300.s0275_h_index_ii.Solution Maven / Gradle / Ivy

package g0201_0300.s0275_h_index_ii;

// #Medium #Array #Binary_Search #Binary_Search_II_Day_8
// #2022_07_06_Time_0_ms_(100.00%)_Space_52.9_MB_(13.67%)

/**
 * 275 - H-Index II\.
 *
 * Medium
 *
 * Given an array of integers `citations` where `citations[i]` is the number of citations a researcher received for their ith paper and `citations` is sorted in an **ascending order** , return compute the researcher's `h` **\-index**.
 *
 * According to the [definition of h-index on Wikipedia](https://en.wikipedia.org/wiki/H-index): A scientist has an index `h` if `h` of their `n` papers have at least `h` citations each, and the other `n − h` papers have no more than `h` citations each.
 *
 * If there are several possible values for `h`, the maximum one is taken as the `h` **\-index**.
 *
 * You must write an algorithm that runs in logarithmic time.
 *
 * **Example 1:**
 *
 * **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, their h-index is 3. 
 *
 * **Example 2:**
 *
 * **Input:** citations = [1,2,100]
 *
 * **Output:** 2 
 *
 * **Constraints:**
 *
 * *   `n == citations.length`
 * *   1 <= n <= 105
 * *   `0 <= citations[i] <= 1000`
 * *   `citations` is sorted in **ascending order**.
**/
public class Solution {
    public int hIndex(int[] citations) {
        int lo = 1;
        int hi = 1000;
        int ans = 0;
        while (lo <= hi) {
            int mid = (lo + hi) / 2;
            int p = check(mid, citations);
            if (citations.length - p >= mid) {
                ans = mid;
                lo = mid + 1;
            } else {
                hi = mid - 1;
            }
        }
        return ans;
    }

    private int check(int v, int[] arr) {
        int lo = 0;
        int hi = arr.length - 1;
        while (lo <= hi) {
            int mid = (lo + hi) / 2;
            if (arr[mid] < v) {
                lo = mid + 1;
            } else {
                hi = mid - 1;
            }
        }
        return lo;
    }
}