ranksort2.cpp

datastucutre and algorithms, application, in C

// rank sort without additional array
#include <iostream>
#include <algorithm> // has copy

using namespace std;


template<class T>
void rearrange(T a[], int n, int r[])
{// In-place rearrangement into sorted order.
   for (int i = 0; i < n; i++)
      // get proper element to a[i]
      while (r[i] != i)
      {
         int t = r[i];
         swap(a[i], a[t]);
         swap(r[i], r[t]);
      }
}

template<class T>
void rank(T a[], int n, int r[])
{// Rank the n elements a[0:n-1].
 // Element ranks returned in r[0:n-1]
   for (int i = 0; i < n; i++)
      r[i] = 0;  // initialize

   // compare all element pairs
   for (int i = 1; i < n; i++)
      for (int j = 0; j < i; j++)
         if (a[j] <= a[i]) r[i]++;
         else r[j]++;
}

int main()
{
   int a[6] = {2, 6, 4, 3, 1, 5};
   int r[6];

   // output the elements
   cout << "a[0:5] = ";
   copy(a, a+6, ostream_iterator<int>(cout, " "));
   cout << endl;

   // sort
   rank(a,6,r);
   rearrange(a,6,r);

   // output the sorted sequence
   cout << "After the sort, a[0:5] = ";
   copy(a, a+6, ostream_iterator<int>(cout, " "));
   cout << endl;
   return 0;
}