subroutine i4vec_sort_heap_a ( n, a ) !*****************************************************************************80 ! !! I4VEC_SORT_HEAP_A ascending sorts an I4VEC using heap sort. ! ! Licensing: ! ! This code is distributed under the GNU LGPL license. ! ! Modified: ! ! 15 April 1999 ! ! Author: ! ! John Burkardt ! ! Reference: ! ! A Nijenhuis and H Wilf, ! Combinatorial Algorithms, ! Academic Press, 1978, second edition, ! ISBN 0-12-519260-6. ! ! Parameters: ! ! Input, integer ( kind = 4 ) N, the number of entries in the array. ! ! Input/output, integer ( kind = 4 ) A(N). ! On input, the array to be sorted; ! On output, the array has been sorted. ! implicit none integer ( kind = 4 ) n integer ( kind = 4 ) a(n) integer ( kind = 4 ) n1 if ( n <= 1 ) then return end if ! ! 1: Put A into descending heap form. ! call i4vec_heap_d ( n, a ) ! ! 2: Sort A. ! ! The largest object in the heap is in A(1). ! Move it to position A(N). ! call i4_swap ( a(1), a(n) ) ! ! Consider the diminished heap of size N1. ! do n1 = n-1, 2, -1 ! ! Restore the heap structure of A(1) through A(N1). ! call i4vec_heap_d ( n1, a ) ! ! Take the largest object from A(1) and move it to A(N1). ! call i4_swap ( a(1), a(n1) ) end do return end