UVA 10200 Prime Time

Test instructions: Give you two numbers, A, B, to find out how many numbers in [A, b] satisfy F (n) =n*n+n+41 is a prime number.

Solving: preprocessing except prefix and, direct

#include <cstring> #include <cstdio> #include <iostream> #include <algorithm> #include < cmath> #include <stack> #include <vector> #define N 10010using namespace Std;int n;int s[n];bool ok (int x) { C0/>if (x==1| | X==0) return false;    for (int i=2; i*i<=x; i++) {        if (x%i==0) return false;    }    return true;} void Init () {for    (int i=0; i<n; i++) {        int k=i*i+i+41;        if (ok (k)) s[i]=1;        else  s[i]=0;    }    for (int i=1; i<n; i++) s[i]+=s[i-1];} int main () {    //freopen ("test.in", "R", stdin);    Init ();    int a, B;    while (~SCANF ("%d%d", &a,&b)) {        int x=b-a+1;        int y=s[b];        if (a!=0)            y-=s[a-1];        Double ans=y*100.0/(x*1.0) +1e-5;//precision        printf ("%.2f\n", ans);    return 0;}

UVA 10200 Prime Time