// プログラミングのお題スレ Part9 [無断転載禁止]©2ch.net
// 31 名前:◆QZschizo.iSO [sage]: 2016/12/31(土) 18:31:14.25 ID:nvhfPpJn
// 瞬速年忘れ問題
// 2017は素数か?素数なら何番目か?
#include<stdio.h>
#include<math.h>
int is_sosu(int d)
{
int i, limit;
if (d == 2) {
return 1;
}
if (d < 2 || d % 2 == 0) {
return 0;
}
limit
= (int) sqrt((double) d
); for (i = 3; i <= limit; i += 2) {
if (d % i == 0) {
return 0;
}
}
return 1;
}
int main()
{
int n, m, count;
while (1) {
if (n == 0) {
return 0;
}
if (is_sosu(n) == 0) {
} else {
count = 1;
for (m = n; m > 2; m -= 2) {
if (is_sosu(m)) {
count++;
}
}
printf(" %d は %d番目の素数\n", n
, count
); }
}
}
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