void heapsort(int arr, unsigned int N)
 {
     unsigned int n = N, i = n/2, parent, child;
     int t;
 
     for (;;) { /* Loops until arr is sorted */
         if (i > 0) { /* First stage - Sorting the heap */
             i--;           /* Save its index to i */
             t = arr;    /* Save parent value to t */
         } else {     /* Second stage - Extracting elements in-place */
             n--;           /* Make the new heap smaller */
             if (n == 0) return; /* When the heap is empty, we are done */
             t = arr;    /* Save last value (it will be overwritten) */
             arr = arr; /* Save largest value at the end of arr */
         }
 
         parent = i; /* We will start pushing down t from parent */
         child = i*2 + 1; /* parent's left child */
 
         /* Sift operation - pushing the value of t down the heap */
         while (child < n) {
             if (child + 1 < n  &&  arr > arr) {
                 child++; /* Choose the largest child */
             }
             if (arr > t) { /* If any child is bigger than the parent */
                 arr = arr; /* Move the largest child up */
                 parent = child; /* Move parent pointer to this child */
                 child = parent*2 + 1; /* Find the next child */
             } else {
                 break; /* t's place is found */
             }
         }
         arr = t; /* We save t in the heap */
     }
 }