[Codility] Lesson 10 - CountFactor

Task discription

A positive integer D is a factor of a positive integer N if there exists an integer M such that N = D * M.

For example, 6 is a factor of 24, because M = 4 satisfies the above condition (24 = 6 * 4).

Write a function:

class Solution { public int solution(int N); }

that, given a positive integer N, returns the number of its factors.

For example, given N = 24, the function should return 8, because 24 has 8 factors, namely 1, 2, 3, 4, 6, 8, 12, 24. There are no other factors of 24.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [1..2,147,483,647].

Source code

#include <algorithm>

int solution(int N) {
    int ans = 0;
    for(long long i=1;i*i<=N;i++) {
        if(N%i == 0) {
            if(i*i == N) ans++;
            else ans += 2;
        }
    }

    return ans;
}

Review

소수 구하기랑 비슷하게 풀면 된다.