mirror of https://github.com/TheAlgorithms/C
123 lines
2.8 KiB
C
123 lines
2.8 KiB
C
/**
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* @file
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* \brief Compute factorial of arbitrarily large numbers by
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* storing individual digits in a byte.
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* \author [Krishna Vedala](https://github.com/kvedala)
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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/**
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* dynamically large number
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*/
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typedef struct _large_num
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{
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char *digits; /**< array to store individual digits */
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unsigned int num_digits; /**< number of digits in the number */
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} large_num;
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/**
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* create a new large number
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* \returns pointer to a large number
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*/
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large_num *new_number(void)
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{
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large_num *new_num = (large_num *)malloc(sizeof(large_num));
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new_num->num_digits = 1;
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new_num->digits = (char *)malloc(1 * sizeof(char));
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new_num->digits[0] = 1;
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return new_num;
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}
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/**
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* delete all memory allocated for large number
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* \param[in] num pointer to large_num to delete
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*/
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void delete_number(large_num *num)
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{
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free(num->digits);
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free(num);
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}
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/**
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* add a digit to the large number
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* \param[in,out] num
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* \param[in] value value of the digit to insert
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*/
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void add_digit(large_num *num, unsigned int value)
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{
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if (value > 9)
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{
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fprintf(stderr, "digit > 9!!\n");
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delete_number(num);
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exit(EXIT_FAILURE);
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}
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num->num_digits++;
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num->digits = (char *)realloc(num->digits, num->num_digits * sizeof(char));
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num->digits[num->num_digits - 1] = value;
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}
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/**
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* multiply large number with another integer and
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* store the result in the same large number
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*/
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void multiply(large_num *num, unsigned long n)
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{
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int i;
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unsigned long carry = 0, temp;
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for (i = 0; i < num->num_digits; i++)
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{
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temp = num->digits[i] * n;
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temp += carry;
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if (temp < 10)
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carry = 0;
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else
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{
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carry = temp / 10;
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temp = temp % 10;
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}
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num->digits[i] = temp;
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}
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while (carry != 0)
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{
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add_digit(num, carry % 10);
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carry /= 10;
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}
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}
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/**
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* main function
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*/
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int main(int argc, char *argv[])
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{
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int number, i;
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// Asks for the number/position of term in Fibonnacci sequence
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if (argc == 2)
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number = atoi(argv[1]);
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else
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{
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printf("Enter the value of n(n starts from 0 ): ");
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scanf("%d", &number);
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}
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large_num *result = new_number();
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clock_t start_time = clock();
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for (i = 2; i <= number; i++) /* Multiply every number from 2 thru N */
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multiply(result, i);
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double time_taken = (clock() - start_time) * (double)1e3 / CLOCKS_PER_SEC;
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// time_taken = (clock() - start_time) / (double) CLOCKS_PER_SEC;
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printf("%d! = ", number);
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for (i = result->num_digits; i > 0; i--)
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putchar(result->digits[i - 1] + '0');
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printf("\nTime taken: %.4g ms\n", time_taken);
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delete_number(result);
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return 0;
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}
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