275. H-Index II.md

275. H-Index II

---

leetcode Daily Challenge on June 18, 2020

---

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?

---

Solution

• mine
  • Java
    • Binary Search Runtime: 0 ms, faster than 100.00%, Memory Usage: 46.6 MB, less than 80.49% of Java online submissions

      // O(logN)time O(1)space
      public int hIndex(int[] citations) {
          int len = citations.length;;
          int s = 0, e = len;
          while (s < e) {
              int m = (s + e) / 2;
              if (citations[m] >= len - m) {
                  e = m;
              } else {
                  s = m + 1;
              }
          }
          return len - s;
      }
      

---