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  1. //make a program to take an array and tell all sum of number of prime factors of it..
  2. //so make a seive array of the least prime factor of all numbers
  3. #include<bits/stdc++.h>
  4. using namespace std;
  5. #define n 1000000
  6. int main(){
  7.  
  8.     vector<int> leasp(n,0);
  9.     leasp[0]=0;
  10.     leasp[1]=0;
  11.     for(int i=2;i*i<n;i++)
  12.     {
  13.         if(leasp[i]==0){//the inner loop would run only for primes
  14.             for(int j=i*i;j<n;j+=i)
  15.             {
  16.                 if(leasp[j]==0){
  17.                     leasp[j]=i;
  18.                 }
  19.             }
  20.         }
  21.     }
  22.     //then for all of the primes we have to put that value to it
  23.     for(int i=2;i<n;i++)
  24.     {
  25.         if(leasp[i]==0)
  26.         {
  27.             leasp[i]=i;
  28.         }
  29.     }
  30.     for(int i=0;i<50;i++)
  31.     {
  32.  
  33.         cout<<leasp[i]<< " ";
  34.     }
  35. }
  36.  
Success #stdin #stdout 0.01s 6912KB
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stdin
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Standard input is empty
stdout
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0 0 2 3 2 5 2 7 2 3 2 11 2 13 2 3 2 17 2 19 2 3 2 23 2 5 2 3 2 29 2 31 2 3 2 5 2 37 2 3 2 41 2 43 2 3 2 47 2 7
https://ideone.com/mJ4xSS
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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