[数值计算] 批处理递归算法示例：

@echo off
set /a n=m=1
set bat="%~0"
setlocal enabledelayedexpansion
set "next=if ^!n^! leq 12 (set /a m*=n,n+=1&echo ^!next^!>>^!bat^!) else (echo ^!m^!&pause&exit)"
(echo;&echo !next!)>>!bat!
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@echo off
set /p inp="1-7: "
call :next %inp% a c b
pause
:next
if %1 equ 0 goto :eof
set /a now=%1-1
call :next %now% %2 %4 %3
echo,%1 from  %2  to  %3
set /a now=%1-1
call :next %now% %4 %3 %2
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@echo off
call:perm "a b c xy z"
pause

:perm <"c1 c2 ..."> // code by plp
setlocal enabledelayedexpansion&set "s=%~1 "
if "!s: =!" == ""  (echo %~2)else for %%b in (%~1)do call:perm "!s:%%b =!" "%~2 %%b"
endlocal&goto:eof
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@echo off
call:perm "1 2 3 4 5 6"
pause

:perm <"c1 c2 ..."> // code by plp
set "s=%~1 "
if "%s: =%" == ""  (echo %~2 &goto:eof)
for %%b in (%~1) do (call:perm "%%s:%%b =%%" "%~2%%b" &set "s=%~1 ")
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@echo off
setlocal enabledelayedexpansion
set total=1
call :lp 16
echo %total%
pause>nul&exit
:lp
set /a num=%1
if %num% neq 0 (
   set /a total*=num,num-=1&call :lp !num!
)
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@echo off
Rem Combination.bat by Paktc
call :func "abcd" ""
pause &exit

:func
 setlocal
   if %1=="" (
     if not %2=="" (echo %~2)
     goto :eof
   )
   set strnow=%~1
   call :func "%strnow:~1%" "%~2%strnow:~0,1%"
   call :func "%strnow:~1%" "%~2"
 endlocal
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