POJ 3518 Prime Gap

Prime Gap

1#include <cmath>2#include <cstdio>3#include <algorithm>4#include <iostream>5#include <string>6#include <cstring>7#include <vector>8 using namespacestd;9 #defineMax 100000Ten intprime[max+5]; One //bool vis[max+5]; A voidGet_prime (intN) { -     //memset (vis,false,sizeof (Vis)); -prime[0]=2; theprime[1]=2; -     intI=3, index=2; -      for(; index<=n;i+=2){ -         //cout<<i<<endl; +         //cout<<prime[index-1]<<endl; -         intHALF=SQRT (i*1.0)+1; +         intj=1; A          while(J<index&&half>prime[j]) {//do not know why J<index can be removed. It's also right to get rid of it.  at             //cout<<i<< "" <<j<< "" <<prime[j]<<endl; -             if(i%prime[j]==0){ -                  Break; -             } -J + +; -         } in         if(half<=Prime[j]) { -prime[index++]=i; to         } +     } -     //cout<<prime[index-1]<<endl; the } * intMain () { $     intN;Panax Notoginseng get_prime (max); -      while(cin>>n&&N) { the         intI=1; +          while(prime[i]<N) { Ai++; the         } +         if(prime[i]==N) { -cout<<0<<Endl; $         } $         Else{ -cout<<prime[i]-prime[i-1]<<Endl; -         } the     } -     return 0;Wuyi}

Time Limit: 5000MS		Memory Limit: 65536K
Total Submissions: 8766		Accepted: 5148

Description

The sequence of n−1 consecutive composite numbers (positive integers that is not prime and is equal to 1) lying betwee N-successive prime numbers p and p + n is called a prime gap of length n. For Example,‹24, 25, 26, 27, 28›between + is a prime gap of length 6.

Your mission is to write a program to calculate, for a given positive integer K, the length of the prime gap that Contains K. For convenience, the length was considered 0 in case no prime gap contains K.

Input

The input is a sequence of lines each of which contains a single positive integer. Each positive integer was greater than 1 and less than or equal to the 100000th prime number, which is 1299709. The end of the input is indicated by a line containing a single zero.

Output

The output should is composed of lines each of the which contains a single non-negative integer. It is the length of the prime Gap, the contains the corresponding positive integer in the input if it is a composite numbe R, or 0 otherwise. No Other characters should occur in the output.

Sample Input

10112724921700

Sample Output

4060114

Source

Japan 2007 Analysis:

POJ 3518 Prime Gap