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pmult.c
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pmult.c
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#include <stdio.h>
#include <stdlib.h>
unsigned long long multiply_digits(unsigned long long n)
{
/*
* return the product of all digits in n
*/
unsigned long long product = 1;
while (n > 0)
{
product *= (n % 10);
n /= 10;
}
return product;
}
unsigned int multiplicative_persistence(unsigned long long n)
{
/*
* return the number of rounds n can pass
*/
unsigned int levels = 0;
while (n > 9) {
levels++;
n = multiply_digits(n);
}
return levels;
}
int main(int argc, char **argv)
{
/*
* best is the current best number for persistent multiplication
* best_levels is how many rounds the best number passed current is
* the current number being tested current_levels is the number of
* rounds the current number passes max is the maximum number to test
* min is the minimum number to test
*/
unsigned long long int best = 0;
unsigned int best_levels = 0;
unsigned long long int current;
unsigned int current_levels;
unsigned long long int max;
unsigned long long int min;
/*
* checking args
*/
if ((argc < 2) || (argc > 3)) {
fprintf(stderr, "usage: %s min max OR %s number\n", argv[0],
argv[0]);
return EXIT_FAILURE;
}
if (argc == 2) {
current = strtoull(argv[1], NULL, 10);
printf("Number: %llu\nLevels: %u\n", current,
multiplicative_persistence(current));
return EXIT_SUCCESS;
}
if (argc == 3) {
min = strtoull(argv[1], NULL, 10);
max = strtoull(argv[2], NULL, 10);
/*
* checking numbers from min to max
*/
for (current = min; current <= max; current++) {
current_levels = multiplicative_persistence(current);
if (current_levels > best_levels) {
best = current;
best_levels = current_levels;
}
}
}
printf("Best Number: %llu\nLevels: %u\n", best, best_levels);
return EXIT_SUCCESS;
}