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  1. #include<iostream>
  2. #include<fstream>
  3. #include<vector>
  4. #include<algorithm>
  5. using namespace std;
  6. ifstream fin("prime.inp");
  7. ofstream fout("prime.out");
  8. int get(int n,vector<int>& x,int len){
  9.     vector<int> bit(len);
  10.     int num=0;
  11.     int c=1;
  12.     for(int i=0;i<len;i++){
  13.         if(n%2==0){
  14.             bit[i]=0;
  15.         }
  16.         else{
  17.             bit[i]=1;
  18.         }
  19.         n=n/2;
  20.         if(bit[i]==1){
  21.             num=num+x[i]*c;
  22.             c=c*10;
  23.         }
  24.     }
  25.     return num;
  26. }
  27. int check(int num){
  28.     if(num<2){
  29.         return 0;
  30.     }
  31.     for(int i=2;i*i<=num;i++){
  32.         if(num%i==0){
  33.             return 0;
  34.         }
  35.     }
  36.     return 1;
  37. }
  38. int main(){
  39.     int n;
  40.     fin>>n;
  41.     int a=1;
  42.     int len=0;
  43.     vector<int> x;
  44.     while(n>0){
  45.         len++;
  46.         a=a*2;
  47.         x.push_back(n%10);
  48.         n=n/10;
  49.     }
  50.     int Max=-1;
  51.     for(int i=1;i<a;i++){
  52.         int num=get(i,x,len);
  53.         if(check(num)==1&&num>Max){
  54.             Max=num;
  55.         }
  56.     }
  57.     fout<<Max;
  58. }
  59.  
Success #stdin #stdout 0s 5312KB
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https://ideone.com/pvgCQS
language:
C++ (gcc 8.3)
created:
2 hours ago
visibility:
public

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