精通递归程序设计

				
int factorial(int n)
{
   return n * factorial(n - 1);
}

				
int factorial(int n)
{
   if(n == 1)
   {
      return 1;
   }
   else
   {
      return n * factorial(n - 1);
   }
}

				
 function sum_list(list l)
    is l null?
       yes - the sum of an empty list is 0 - return that
    data = head of list l
    rest_of_list = rest of list l
    the sum of the list is:
       data + sum_list(rest_of_list)

				
 (define sum-list (lambda (l)
    (if (null? l)
       0
       (let (
             (data (car l))
             (rest-of-list (cdr l)))
          (+ data (sum-list rest-of-list))))))

				
int sum_list(struct list_node *l)
{
   if(l == NULL)
      return 0;
    return l.data + sum_list(l.next);
}

				
(define is-in-list
    (lambda   (the-list the-string)
       ;;Check for base case of "list empty"
       (if (null? the-list)
          #f
          ;;Check for base case of "found item"
          (if (equal? the-string (car the-list))
             #t
             ;;Run the algorithm on a smaller problem
             (is-in-list (cdr the-list) the-string)))))

				
 (define is-in-list2
    (lambda (the-list the-string)
       (letrec
         (
              (recurse (lambda (internal-list)
                   (if (null? internal-list)
                      #f
                      (if (equal? the-string (car internal-list))
                         #t
                         (recurse (cdr internal-list)))))))
          (recurse the-list))))

				
(define is-in-list2
    (lambda (the-list the-string)
       ;;Named Let
       ;;This let block defines a function called "recurse" that is the
      ;;body of this let.  The function's parameters are the same as
       ;;the variables listed in the let.
       (let recurse
          ;;internal-list is the first and only parameter.  The
          ;;first time through the block it will be primed with
          ;;"the-list" and subsequent calls to "recurse" will
          ;;give it whatever value is passed to "recurse"
          ( (internal-list the-list) )

          ;;Body of function/named let block
          (if (null? internal-list)
             #f
             (if (equal? the-string (car internal-list))
                #t
                ;;Call recursive function with the
                ;;rest of the list
                (recurse (cdr internal-list)))))))

				
(define is-ascending
    (lambda (the-list)
       ;;First, Initialize the algorithm.  To do this we
       ;;need to get the first value, if it exists, and
       ;;use it as a seed to the recursive function
       (if (null? the-list)
          #t
          (let is-ascending-recurse
             (
                 (previous-item (car the-list))
                (remaining-items (cdr the-list))
             )
             ;;Base case #1 - end of list
             (if (null? remaining-items)
                #t
                (if (< previous-item (car remaining-items))
                   ;;Recursive case, check the rest of the list
                   (is-ascending-recurse (car remaining-items) (cdr remaining-items))
                   ;;Base case #2 - not in ascending order
                   #f))))))

				
void print_report(struct report_line *report_lines, int num_lines)
{
   int num_lines_this_page = 0;
   int page_number = 1;
    int current_line; /* iterates through the lines */
    int current_group = 0; /* tells which grouping we are in */
    int previous_group = 0; /* tells which grouping was here on the last loop */
    int group_total = 0; /* saves totals for printout at the end of the grouping */

     print_headings(page_number);

     for(current_line = 0; current_line < num_lines; current_line++)
    {
       num_lines_this_page++;
        if(num_lines_this_page == LINES_PER_PAGE)
       {
          page_number++;
          page_break();
          print_headings(page_number);
       }

       current_group = get_group(report_lines[current_line]);
       if(current_group != previous_group)
       {
         print_totals_for_group(group_total);
          group_total = 0;
       }

        print_line(report_lines[current_line]);

       group_total += get_line_amount(report_lines[current_line]);
    }
}

				
void print_report(struct report_line *report_lines, int num_lines)
{
    int num_lines_this_page = 0;
    int page_number = 1;
    int current_line; /* iterates through the lines */
    int current_group = 0; /* tells which grouping we are in */
    int previous_group = 0; /* tells which grouping was here on the last loop */
    int group_total = 0; /* saves totals for printout at the end of the grouping */

      /* initialize */
   print_headings(page_number);

     /* Seed the values */
    print_report_i(report_lines, 0, 1, 1, 0, 0, num_lines);
}

void print_report_i(struct report_line *report_lines, /* our structure */
    int current_line, /* current index into structure */
    int num_lines_this_page, /* number of lines we've filled this page */
    int page_number,
     int previous_group, /* used to know when to print totals */
    int group_total, /* current aggregated total */
    int num_lines) /* the total number of lines in the structure */
{
    if(current_line == num_lines)
    {
       return;
    }
    else
    {
       if(num_lines_this_page == LINES_PER_PAGE)
       {
          page_break();
          print_headings(page_number + 1);
          print_report_i(
             report_lines,
              current_line,
              1,
              page_number + 1,
              previous_group,
              group_total,
              num_lines);
       }
       else
       {
          int current_group = get_group(report_lines[current_line]);
          if(current_group != previous_group && previous_group != 0)
          {
             print_totals_for_group(group_total);
             print_report_i(
                report_lines,
                 current_line,
                 num_lines_this_page + 1,
                 page_number,
                 current_group,
                 0,
                 num_lines);
          }
          else
          {
             print_line(report_lines[current_line]);
             print_report_i(
                report_lines,
                 current_line + 1,
                 num_lines_this_page + 1,
                 page_number,
                 current_group,
                 group_total + get_line_amount(report_lines[current_line]),
                 num_lines);
          }
       }
    }
}