翱翔云天

*Store where the queen is
DATA: BEGIN OF row ,
           val TYPE i,
         END OF row .
DATA: i_row LIKE row OCCURS 0 WITH HEADER LINE .

*How many ways we can achieve
DATA: oktimes TYPE i .
data: queen type i.

*Define the number of queen
CONSTANTS: queenmax TYPE i VALUE 8 .

*Input queen number
PARAMETERS: p_num TYPE i DEFAULT queenmax.

START-OF-SELECTION .
  PERFORM main_process .

*&———————————————————————*
*& Form MAIN_PROCESS
*&———————————————————————*
* text
*———————————————————————-*
FORM main_process .
  DATA: l_num TYPE i . "The first place
  DATA: l_s(50) TYPE c . "Output string
  DATA: l_time(10) TYPE c.

  queen = p_num + 1.
* Init place table
  DO queenmax TIMES .
    i_row-val = -1 .
    APPEND i_row .
  ENDDO.
  l_num = 1 .
* recursion
  PERFORM place_queen USING l_num.

* Get ways of algorithm

  l_time = oktimes .
  CONDENSE l_time .
  CONCATENATE ‘Eight Queens have’ l_time ‘ways to solve it.’ INTO l_s
  SEPARATED BY space.
  WRITE: l_s .
ENDFORM. " MAIN_PROCESS
*&———————————————————————*
*& Form place_queen
*&———————————————————————*
* text
*———————————————————————-*
FORM place_queen USING p_num.
* Local data definition
  DATA: l_i TYPE i .
  DATA: l_num TYPE i .
* Temp variants
  DATA: l_k TYPE i .
  DATA: l_t1 TYPE i .
  DATA: l_t2 TYPE i .

* Safe place
  DATA: BEGIN OF qsave OCCURS 0 ,
    val TYPE i ,
  END OF qsave .

* Init safe place, make all place be safe
  DO queenmax TIMES .
    qsave-val = 1 .
    APPEND qsave .
  ENDDO.

  l_i = 1 .
  l_num = p_num .

* This loop get the safe place
  WHILE l_i < l_num .
    READ TABLE i_row INDEX l_i .
    READ TABLE qsave INDEX i_row-val .
    qsave-val = 0 .
    MODIFY qsave INDEX i_row-val.

    l_k = l_num - l_i .
    l_t1 = i_row-val + l_k .
    l_t2 = i_row-val - l_k .

* Mark safe place
* If a queen’s place is I_ROW[i]=j, then the unsafe place is row k column j
* and column j+k-i and j-k+i

    IF l_t1 >= 1 AND l_t1 < queen .
      READ TABLE qsave INDEX l_t1 .
      qsave-val = 0 .
      MODIFY qsave INDEX l_t1 .
    ENDIF.

    IF l_t2 >= 1 AND l_t2 < queen .
      READ TABLE qsave INDEX l_t2 .
      qsave-val = 0 .
      MODIFY qsave INDEX l_t2 .
    ENDIF.
    l_i = l_i + 1 .
  ENDWHILE .

  l_i = 1 .
* Below loop is to get the queen’s place
  WHILE l_i < queen .
    READ TABLE qsave INDEX l_i .
    IF qsave-val = 0 .
* If this place is not safe, then get the next place
      l_i = l_i + 1 .
      CONTINUE .
    ENDIF.

* if not the last place
    IF p_num < queenmax.
      READ TABLE i_row INDEX p_num .
      i_row-val = l_i .
      MODIFY i_row INDEX p_num .
      l_num = p_num + 1 .
* Get the next queen’s place
      PERFORM place_queen USING l_num .
    ELSE .
* The last queen, give her the last place
      READ TABLE i_row INDEX p_num .
      i_row-val = l_i .
      MODIFY i_row INDEX p_num.
* The ways of place add 1 and output
      oktimes = oktimes + 1 .
      WRITE: ‘——————————————————————————–’,/.
      LOOP AT i_row .
        WRITE: i_row-val .
      ENDLOOP .
      WRITE: / .
    ENDIF.
    l_i = l_i + 1 .
  ENDWHILE .
ENDFORM. " PLACE_QUEEN