How to obtain the index permutation after the sorting

Question

Given an array arr = {5, 16, 4, 7}, we can sort it through sort(arr, arr+sizeof(arr)/sizeof(arr[0])). so now the array arr = {4, 5, 7, 16}

Answer 1

I think we can solve this problem without using vector. I'm newbie, to be honest, i don't understand what you wrote above, and all of you used vector which i will study later :))) ( i'm lazy) Here's my way :

// First, copy array a[] to array b[]

   void copyarray(double b[],double a[],int n){
     for(int i=0;i<n;i++)b[i]=a[i];
    }

// Second, sort array a[] ( decrease )

/*Third, " sorter " array a[], that means: in array a[],if there exists same values, they will merge into one ! i will set array o[] is "the sorted array a[] " */

 void sorter(double o[],double a[],int n,int &dem){   
     int i;
     o[0]=a[0];
     for(i=1;i<n;i++){
        if(a[i]!=a[i-1]){
          dem++; o[dem]=a[i];
         }
      }
      dem++;
 }

/* 4th, our main goal: get the index: i will put the index into array c[] */

void index_sort(double o[],double b[], double c[], int dem, int n){
    int i,j,chiso=0;
    for(j=0;j<dem;j++){
       for(i=0;i<n;i++){
          if(b[i]==o[j]){
             c[chiso]=i;
             chiso++;
           }
        }
     }
 }

  // DONE!
 int main(){
        int n,dem=0;
         double a[100],b[100],c[100],o[100];
         cin>>n;
         input(a,n);
         copyarray(b,a,n);
         copyarray(c,a,n);
         sort(a,n);
         sorter(o,a,n,dem); 
         index_sort(o,b,c,dem,n); 
         for(int i=0;i<n;i++) cout<<c[i]<<" ";
   }