From fe0c2b8517e17b30f10c24793112ac6817bca214 Mon Sep 17 00:00:00 2001
From: Krishna Vedala <krishna.vedala@ieee.org>
Date: Fri, 1 May 2020 23:12:38 -0400
Subject: [PATCH] compute factorial of arbitrarily any number

---
 others/large_factorial.cpp | 128 +++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 others/large_factorial.cpp

diff --git a/others/large_factorial.cpp b/others/large_factorial.cpp
new file mode 100644
index 000000000..ef9b68feb
--- /dev/null
+++ b/others/large_factorial.cpp
@@ -0,0 +1,128 @@
+#include <iostream>
+#include <chrono>
+#include <vector>
+
+using namespace std;
+
+/**
+ * Store large unsigned numbers as a C++ vector
+ * The class provides convenience functions to add a
+ * digit to the number, perform multiplication of
+ * large number with long unsigned integers.
+ **/
+class large_number
+{
+public:
+    large_number() /**< initializer */
+    {
+        _digits.push_back(1);
+    }
+
+    /**
+     * add a digit to the large number
+     **/
+    void add_digit(unsigned int value)
+    {
+        if (value > 9)
+        {
+            fprintf(stderr, "digit > 9!!\n");
+            exit(EXIT_FAILURE);
+        }
+
+        _digits.push_back(value);
+    }
+
+    /**
+     * Get number of digits in the number
+     **/
+    const size_t num_digits() const
+    {
+        return _digits.size();
+    }
+
+    /**
+     * operator over load to access the
+     * i^th digit conveniently and also
+     * assign value to it
+     **/
+    unsigned char &operator[](size_t n)
+    {
+        return this->_digits[n];
+    }
+
+    /**
+     * multiply large number with another integer and
+     * store the result in the same large number
+     **/
+    void multiply(const unsigned long n)
+    {
+        size_t i;
+        unsigned long long carry = 0, temp;
+        for (i = 0; i < this->num_digits(); i++)
+        {
+            temp = (*this)[i] * n;
+            temp += carry;
+            if (temp < 10)
+                carry = 0;
+            else
+            {
+                carry = temp / 10;
+                temp = temp % 10;
+            }
+            (*this)[i] = temp;
+        }
+
+        while (carry != 0)
+        {
+            this->add_digit(carry % 10);
+            carry /= 10;
+        }
+    };
+
+    /**
+     * print the large number
+     **/
+    void print()
+    {
+        for (size_t i = num_digits(); i > 0; i--)
+            putchar(_digits[i - 1] + '0');
+    };
+
+private:
+    vector<unsigned char> _digits; /**< where individual digits are stored */
+};
+
+/**
+ * Main program
+ **/
+int main(int argc, char *argv[])
+{
+    int number, i;
+
+    //Asks for the number/position of term in Fibonnacci sequence
+    if (argc == 2)
+        number = atoi(argv[1]);
+    else
+    {
+        printf("Enter the value of n(n starts from 0 ): ");
+        scanf("%d", &number);
+    }
+
+    large_number result;
+
+    auto start_time = chrono::high_resolution_clock::now();
+    for (i = 2; i <= number; i++)
+        /* Multiply every number from 2 thru N */
+        result.multiply(i);
+    auto end_time = chrono::high_resolution_clock::now();
+    chrono::duration<double> time_taken = end_time - start_time;
+
+    cout << number << "! = ";
+    result.print();
+    cout << endl
+         << "Number of digits: " << result.num_digits() << endl
+         << "Time taken: " << time_taken.count() << " s"
+         << endl;
+
+    return 0;
+}