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Euler Project (in C)
/*
Copyright 2016 strupo
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
/* Euler Project - Problem 1 */
int main (void)
{
int i; /* counter */
int start = 0; /* start summing from here */
int stop = 1e3; /* stop summing when you reach this */
int mult[2]; /* this array contains the numbers whose multiples will be summed */
long sum = 0L; /* will contain the sum; initialized to zero */
mult[0] = 3;
mult[1] = 5;
for (i = start; i < stop; ++i) {
if (!(i % mult[0] && i % mult[1])) { /* :DDD */
sum += (long) i;
}
}
printf("Sum of multiples of %d and %d from %d to %d = %ld\n",
mult[0], mult[1], start, stop, sum);
return 0;
}
/* vim: set et sts=4 sw=4 ts=8 cin fenc=ascii : */
/*
Copyright 2016 strupo
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
/* Euler Project - Problem 2 */
const long int *fibonacci(const long int max);
int main (void)
{
printf("Sum = %ld\n", *(fibonacci(4e6)));
return 0;
}
const long int *fibonacci(const long int max)
{
static long int sum = 0;
int i, i1, i2;
#ifdef DEBUG
int c;
c = 0;
printf("fib[%*d]\t=\t%*d\n", 4, c++, 6, 0);
#endif /* DEBUG */
i2 = 0;
i1 = 1;
i = 0;
while (i < max) {
i2 = i1;
i1 = i;
i = i1 + i2;
#ifdef DEBUG
printf("fib[%*d]\t=\t%*d\n", 4, c, 6, i);
++c;
#endif /* DEBUG */
if (!(i % 2)) {
sum += i;
}
}
return (const long int *) &sum;
}
/* vim: set et sts=4 sw=4 ts=8 cin fenc=ascii : */
/*
Copyright 2016 strupo
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <math.h>
/* Project Euler - Problem 3 */
int is_prime(unsigned long n);
int main (void)
{
unsigned long num = 600851475143UL;
unsigned long i;
unsigned long max;
max = 1;
for (i = 2; i <= floor(sqrt((double) num)); ++i) {
if (is_prime(i) && !(num % i)) {
max = i;
}
}
printf("Largest prime factor for %ld = %lu\n", num, max);
return 0;
}
int is_prime(unsigned long n)
{
unsigned long i;
int p; /* p != 0 <=> n is not prime */
p = 1;
for (i = 2; i <= floor(sqrt(n)); ++i) {
if (!(n % i)) {
p = 0;
break;
}
}
return p;
}
/* vim: set et sts=4 sw=4 ts=8 cin fenc=ascii : */
/*
Copyright 2016 strupo
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#define MAX_STRING 1<<3
/* Project Euler - Problem 4 */
int is_palindrome(const int n);
char *int_to_string(const int n);
int length_of_string(const char *s);
int find_largest_palindrome(void);
int main (void)
{
int lp; /* largest palindrome */
lp = find_largest_palindrome();
printf("Largest palindrome made from multiplying 3-digit numbers = %d\n", lp);
return 0;
}
int is_palindrome(const int n)
{
int p; /* p = 1 <=> n is a palindrome */
int i; /* counter */
char *s; /* string containing n */
int l; /* length of string s */
s = int_to_string(n);
l = length_of_string(s) - 1;
p = 1; /* Assuming n is a palindrome */
for (i = 0; i <= l / 2; ++i) {
if (s[i] != s[l - i]) {
p = 0;
break;
}
}
return p;
}
char *int_to_string(const int n)
{
int i; /* Number of digits in n */
int l;
int m;
static char s[MAX_STRING] = {'\0'};
m = n;
i = 0;
while (m > 0) {
s[i] = m % 10 + '0';
m /= 10;
++i;
}
l = i - 1;
/* reversing s */
for (i = 0; i < l / 2; ++i) {
int tmp;
tmp = s[i];
s[i] = s[l - i];
s[l - i] = tmp;
}
return s;
}
int length_of_string(const char *s)
{
int i; /* counter */
int l; /* length */
l = i = 0;
while (s[i++]) {
++l;
}
return l;
}
int find_largest_palindrome(void)
{
int i; /* c u t r */
int j; /* o n e s */
int m; /* max */
m = 0;
for (i = 0; i < 1e3; ++i) {
for (j = 0; j < 1e3; ++j) {
if (is_palindrome(i * j)) {
m = i * j > m ? i * j : m;
}
}
}
return m;
}
/* vim: set et sts=4 sw=4 ts=8 cin fenc=ascii : */
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