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+/*
+Challenge 241
+
+Task 2: Prime Order
+Submitted by: Mohammad S Anwar
+
+You are given an array of unique positive integers greater than 2.
+
+Write a script to sort them in ascending order of the count of their prime
+factors, tie-breaking by ascending value.
+Example 1
+
+Input: @int = (11, 8, 27, 4)
+Output: (11, 4, 8, 27))
+
+Prime factors of 11 => 11
+Prime factors of  4 => 2, 2
+Prime factors of  8 => 2, 2, 2
+Prime factors of 27 => 3, 3, 3
+*/
+
+#include <algorithm>
+#include <iostream>
+#include <vector>
+using namespace std;
+
+struct Num {
+    int n;
+    vector<int> factors;
+
+    Num(int n);
+    bool operator<(const Num& other);
+};
+
+bool is_prime(int n) {
+    if (n <= 1)
+        return false;
+    if (n <= 3)
+        return true;
+    if ((n % 2) == 0 || (n % 3) == 0)
+        return false;
+    for (int i = 5; i * i <= n; i += 6)
+        if ((n % i) == 0 || (n % (i + 2)) == 0)
+            return false;
+    return true;
+}
+
+int next_prime(int n) {
+    if (n <= 1)
+        return 2;
+    do {
+        n++;
+    } while (!is_prime(n));
+    return n;
+}
+
+vector<int> prime_factors(int n) {
+    vector<int> out;
+    if (n < 2) {
+        int p = 1;
+        out.push_back(p);
+    }
+    else {
+        int p = 2;
+        while (n > 1) {
+            while (n % p == 0) {
+                out.push_back(p);
+                n /= p;
+            }
+            p = next_prime(p);
+        }
+    }
+    return out;
+}
+
+Num::Num(int n) {
+    this->n = n;
+    this->factors = prime_factors(n);
+}
+
+int num_compare(const Num& a, const Num& b) {
+    int a_size = static_cast<int>(a.factors.size());
+    int b_size = static_cast<int>(b.factors.size());
+    if (a_size != b_size)
+        return a_size - b_size;
+    for (size_t i = 0; i < a_size; i++) {
+        if (a.factors[i] != b.factors[i])
+            return a.factors[i] - b.factors[i];
+    }
+    return 0;
+}
+
+bool Num::operator<(const Num& other) {
+    return num_compare(*this, other) < 0 ? true : false;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc < 2) {
+        cerr << "Usage: ch-2 n n n ..." << endl;
+        exit(EXIT_FAILURE);
+    }
+
+    vector<Num> nums;
+
+    // parse args and compute primes
+    for (int i = 1; i < argc; i++) {
+        int n = atoi(argv[i]);
+        nums.emplace_back(n);
+    }
+
+    // sort
+    sort(nums.begin(), nums.end());
+
+    // output
+    const char* sep = "";
+    for (auto& num : nums) {
+        cout << sep << num.n;
+        sep = " ";
+    }
+}