数据非常小,直接枚举即可!

 

#include<cstdio>
int a[30];
int main(){
    int n=1;
    scanf("%d",&a[n]);
    while (a[n]!=0){
        n++;
        scanf("%d",&a[n]);
    }
    n=n-1;
    int sum=0;
    for (int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if (a[i]==2*a[j]||a[j]==2*a[i])sum++;
    printf("%d\n",sum);
    return 0;
}
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