SAS递归实现二分法查找

SAS 二分法查找

%global MIDNUM TARGETNUM FRONTNUM ENDNUM ERRNUM ii;

%let FRONTNUM=1;
%let TARGETNUM=200;                                                                                                                    
%let ENDNUM=1024;                                                                                                                      
%let ERRNUM=0.5; 
%let ii=0;


%macro search;

%if (%SYSEVALF(%SYSFUNC(ABS(%sysevalf((&FRONTNUM + &ENDNUM)/2) - &TARGETNUM)) > &ERRNUM)) %then %do;  
%let MIDNUM=%sysevalf((&FRONTNUM + &ENDNUM)/2);  

 %let ii= %eval(&ii+1); 
 %PUT &ii ... &MIDNUM ;  
 
%if (%sysevalf(&MIDNUM - &TARGETNUM >0)) %then %do;  
  %LET ENDNUM=&MIDNUM;  
%end;
%else %do;
   %LET FRONTNUM=&MIDNUM;  
%end; 

	 %search;
%end;
%mend;

%search;