43 lines
806 B
C++
43 lines
806 B
C++
#include<iostream>
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#define N 4000
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#define MAX 32770
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using namespace std;
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int su[N],tot;
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void prime()
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{
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tot=1;
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su[0]=2;
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for(int i=3;i<MAX;i+=2)
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{
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int ok=1;
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for(int j=0;j<tot;j++)
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{
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if(su[j]*su[j]>i) break;
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if(i%su[j]==0) {ok=0;break;}
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}
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if(ok) su[tot++]=i;
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}
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}
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int main()
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{
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int n;
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prime();
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while(cin>>n&&n)
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{
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int num=0;
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for(int i=0;2*su[i]<=n;i++)
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{
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int a=0,b=tot;
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while(a<b)
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{
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int mid=(a+b)/2;
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if(su[i]+su[mid]==n) {num++;break;}
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if(su[i]+su[mid]<n) a=mid+1;
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if(su[i]+su[mid]>n) b=mid;
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}
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}
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cout<<num<<endl;
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}
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return 0;
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}
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