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solving Project Euler Problem03 about prime

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koseokkyu 2017-12-04 15:27:24 +09:00
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commit 6d1a0eb3c3
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57
Project Euler/Problem 03/sol1.c Normal file
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/*
Problem:
The prime factors of 13195 are 5,7,13 and 29. What is the largest prime factor of a given number N?
e.g. for 10, largest prime factor = 5. For 17, largest prime factor = 17.
*/
#include <stdio.h>
#include <math.h>
int isprime(int no) {
int sq;
if (no == 2) {
return 1;
}
else if (no%2 == 0) {
return 0;
}
sq = ((int)(sqrt(no))) + 1;
for (int i = 3; i < sq; i + 2) {
if (no%i == 0) {
return 0;
}
}
return 1;
}
int main() {
int maxNumber = 0;
int n = 0;
int n1;
scanf("%d", &n);
if (isprime(n) == 1)
printf("%d", n);
else {
while (n % 2 == 0) {
n = n / 2;
}
if (isprime(n) == 1) {
printf("%d\n", n);
}
else {
n1 = ((int)(sqrt(n))) + 1;
for (int i = 3; i < n1; i + 2) {
if (n%i == 0) {
if (isprime((int)(n / i)) == 1) {
maxNumber = n / i;
break;
}
else if (isprime(i) == 1) {
maxNumber = i;
}
}
}
printf("%d\n", maxNumber);
}
}
}

23
Project Euler/Problem 03/sol2.c Normal file
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/*
Problem:
The prime factors of 13195 are 5,7,13 and 29. What is the largest prime factor of a given number N?
e.g. for 10, largest prime factor = 5. For 17, largest prime factor = 17.
*/
#include <stdio.h>
int main() {
int n = 0;
scanf("%d", &n);
int prime = 1;
int i = 2;
while (i*i <= n) {
while (n%i == 0) {
prime = i;
n /= i;
}
i += 1;
}
if (n > 1)
prime = n;
printf("%d\n", prime);
}