Twin Primes
Twin primes are pairs of primes of the form (p; p + 2). The term \twin prime" was coined by Paul
Stckel (1892-1919). The rst few twin primes are (3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43).
In this problem you are asked to nd out the S-th twin prime pair where S is an integer that will be
given in the input.
Input
The input will contain less than 10001 lines of input. Each line contains an integers S (1 S 100000),
which is the serial number of a twin prime pair. Input le is terminated by end of le.
Output
For each line of input you will have to produce one line of output which contains the S-th twin prime
pair. The pair is printed in the form (p1,<space>p2). Here <space> means the space character (ASCII
32) . You can safely assume that the primes in the 100000-th twin prime pair are less than 20000000.
Sample Input
1
2
3
4
Sample Output
(3, 5)
(5, 7)
(11, 13)
(17, 19)Twin primes are pairs of primes of the form (p; p + 2). The term \twin prime" was coined by Paul
Stckel (1892-1919). The rst few twin primes are (3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43).
In this problem you are asked to nd out the S-th twin prime pair where S is an integer that will be
given in the input.
Input
The input will contain less than 10001 lines of input. Each line contains an integers S (1 S 100000),
which is the serial number of a twin prime pair. Input le is terminated by end of le.
Output
For each line of input you will have to produce one line of output which contains the S-th twin prime
pair. The pair is printed in the form (p1,<space>p2). Here <space> means the space character (ASCII
32) . You can safely assume that the primes in the 100000-th twin prime pair are less than 20000000.
Sample Input
1
2
3
4
Sample Output
(3, 5)
(5, 7)
(11, 13)
(17, 19)
Meaning of the questions:
Defined prime bis (p, p + 2), p, p + 2 are both prime numbers.
First enter a number n, the n-th double prime.
analysis:
Time limit is 3000ms, the amount of data 2e7, violence can be directly solved.
First Euler sieve out all the prime numbers, then violence enumerate all the prime numbers to determine whether the prime number can double.
AC code:
#include<bits/stdc++.h> using namespace std; typedef pair<int,int> P; P p[20000005]; bool u[20000005]; int su[20000005]; int num; void olas() { num=1; memset(u,true,sizeof(u)); for(int i=2;i<=20000000;i++) { if(u[i]) su[num++]=i; for(int j=1;j<num;j++) { if(i*su[j]>20000000) break; u[i*su[j]]=false; if(i%su[j]==0) break; } } } int main() { //freopen("input.txt","r",stdin); int n; olas(); int num=0; for(int i=2;i<=20000000-2;i++) { if(u[i]&&u[i+2]) { p[num++]=P(i,i+2); } } while(~scanf("%d",&n)) { printf("(%d, %d)\n",p[n-1].first,p[n-1].second); } return 0; }