Prime factors

futureskills/primefactors.cpp

@@ -0,0 +1,29 @@
+#include <cstdio>
+#include <cassert>
+#include <vector>
+
+using prime_vec_t = std::vector<int>;
+
+// https://en.wikipedia.org/wiki/Trial_division
+auto prime_factors(int num) -> prime_vec_t {
+    prime_vec_t primes{};
+    int f = 2;
+    while (num > 1) {
+        if (num % f == 0) {
+            primes.emplace_back(f);
+            num = num / f;
+        } else {
+            f += 1;
+        }
+    }
+    return primes;
+}
+
+auto main([[maybe_unused]]int argc, [[maybe_unused]]char const* argv[]) -> int {
+    auto factors = prime_factors(20);
+    for (auto const& factor : factors) {
+        std::printf("%d, ", factor);
+    }
+    std::printf("\n");
+    return 0;
+}