g0201_0300.s0274_h_index.Solution Maven / Gradle / Ivy

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package g0201_0300.s0274_h_index;

// #Medium #Array #Sorting #Counting_Sort #2022_07_06_Time_3_ms_(45.78%)_Space_41.7_MB_(75.73%)

import java.util.Arrays;

/**
 * 274 - H-Index\.
 *
 * Medium
 *
 * Given an array of integers `citations` where `citations[i]` is the number of citations a researcher received for their i^th paper, 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**.
 *
 * **Example 1:**
 *
 * **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, their h-index is 3. 
 *
 * **Example 2:**
 *
 * **Input:** citations = [1,3,1]
 *
 * **Output:** 1 
 *
 * **Constraints:**
 *
 * *   `n == citations.length`
 * *   `1 <= n <= 5000`
 * *   `0 <= citations[i] <= 1000`
**/
public class Solution {
    public int hIndex(int[] citations) {
        // Sort array then traverse from end keep track of counter denoting total elements seen so
        // far
        Arrays.sort(citations);
        int count = 0;
        int hIndex = 0;
        for (int i = citations.length - 1; i >= 0; i--) {
            if (i == citations.length - 1 && count == citations[i]) {
                hIndex = citations[i];
                return hIndex;
                //  Ex:- 7 10--> counter =8
            } else if (citations[i] <= count && count < citations[i + 1]) {
                hIndex = count;
                return hIndex;
                // Ex:- 7 9 --> counter 6 (incuding 7 there willbe 7 elements)
            } else if (citations[i] == count + 1) {
                hIndex = count + 1;
                return hIndex;
            } else {
                count++;
            }
        }
        // case when no element is hindex so far
        if (count < citations[0]) {
            hIndex = count;
        }
        return hIndex;
    }
}