# Daily Coding Challenge #38

Daily Coding Challenge (87 Part Series)

This is a series of Daily Coding Challenge. Each day I show a few solutions written in C++. The questions are from coding practice/contest sites such as HackerRank, LeetCode, Codeforces, Atcoder and etc.

/*
LeetCode - H-Index

Given an array of citations (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 = [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, her h-index is 3.
Note: If there are several possible values for h, the maximum one is taken as the h-index.
*/

class Solution {
public:
int hIndex(vector<int>& citations) {
int n = citations.size();
if(n==0) return 0;
sort(citations.begin(),citations.end());
for(int i=0;i<n;i++){
if(citations[i]>=n-i) return n-i;
}
return 0;
}
};

// [3,0,6,1,5]
// [0,1,2,3,6]
//  1 2 3 4 5


/*
LeetCode - H-Index II

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.

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?
*/

class Solution {
public:
int hIndex(vector<int>& citations) {
// binary search approach
int n = citations.size();
if(n==0) return 0;
int l=0,r=n-1,m;
while(l<=r){
m=l+(r-l)/2;
// there are citations[mid] papers that have at least citations[mid] citations
if(citations[m]==n-m) return citations[m];
// there are citations[mid] papers that have less than citations[mid] citations
else if(citations[m]<n-m) l=m+1;
// there are citations[mid] papers that have more than citations[mid] citations
else r=m-1;
}
return n-r-1;
// or return n-l;
}
};


The source code is available in corresponding repo below. Star and watch for timely updates!

## wingkwong / atcoder

### 🏆 A Collection of my AtCoder Solutions with Explanations 🏆

Daily Coding Challenge (87 Part Series)

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### Wing-Kam

Consultant by day. Developer by night. AWS certified. Exploring #CloudNative currently.