From 04e0acc3cf5f83a6aa018575478b4eee54a9c97f Mon Sep 17 00:00:00 2001
From: Divyajyoti Ukirde <30872426+divyajyotiuk@users.noreply.github.com>
Date: Mon, 5 Oct 2020 18:22:27 +0530
Subject: [PATCH] feat: added check_factorial (#1155)

* feat: added check_factorial

* updating DIRECTORY.md

* feat: added check_factorial

* review changes

* review changes

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
---
 DIRECTORY.md             |  1 +
 math/check_factorial.cpp | 64 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 math/check_factorial.cpp

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 08370c1b2..7e72b439e 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -122,6 +122,7 @@
   * [Armstrong Number](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/armstrong_number.cpp)
   * [Binary Exponent](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/binary_exponent.cpp)
   * [Check Amicable Pair](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/check_amicable_pair.cpp)
+  * [Check Factorial](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/check_factorial.cpp)
   * [Check Prime](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/check_prime.cpp)
   * [Complex Numbers](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/complex_numbers.cpp)
   * [Double Factorial](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/math/double_factorial.cpp)
diff --git a/math/check_factorial.cpp b/math/check_factorial.cpp
new file mode 100644
index 000000000..2170b81a0
--- /dev/null
+++ b/math/check_factorial.cpp
@@ -0,0 +1,64 @@
+/**
+ * @file
+ * @brief A simple program to check if the given number is a factorial of some
+ * number or not.
+ * @author [Divyajyoti Ukirde](https://github.com/divyajyotiuk)
+ */
+#include <cassert>
+#include <iostream>
+
+/**
+ * Function to check if the given number is factorial of some number or not.
+ * @param n number to be checked.
+ * @return if number is a factorial, returns true, else false.
+ */
+
+bool is_factorial(uint64_t n) {
+    if (n <= 0) {
+        return false;
+    }
+    for (uint32_t i = 1;; i++) {
+        if (n % i != 0) {
+            break;
+        }
+        n = n / i;
+    }
+    if (n == 1) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
+/** Test function
+ * @returns void
+ */
+void tests() {
+    std::cout << "Test 1:\t n=50\n";
+    assert(is_factorial(50) == false);
+    std::cout << "passed\n";
+
+    std::cout << "Test 2:\t n=720\n";
+    assert(is_factorial(720) == true);
+    std::cout << "passed\n";
+
+    std::cout << "Test 3:\t n=0\n";
+    assert(is_factorial(0) == false);
+    std::cout << "passed\n";
+
+    std::cout << "Test 4:\t n=479001600\n";
+    assert(is_factorial(479001600) == true);
+    std::cout << "passed\n";
+
+    std::cout << "Test 5:\t n=-24\n";
+    assert(is_factorial(-24) == false);
+    std::cout << "passed\n";
+}
+
+/** Main function
+ * @returns 0 on exit
+ */
+int main() {
+    tests();
+    return 0;
+}