(PL\SQL) How to get MAX(num)+DISTINCT str

CLEAR;  
with t as  
 (
 select '11' num, 'string1' str, '1' DATA from dual union all  
 select '12' num, 'string1' str, '3' DATA from dual union all  
 select '15' num, 'string1' str, '3' DATA from dual union all  
 select '25' num, 'string2' str, '10' DATA from dual union all  
 select '26' num, 'string2' str, '2' DATA from dual union all  
 SELECT '29' num, 'string2' str, '4' DATA from dual  
 )  
SELECT * FROM t  
WHERE num IN (SELECT MAX(num) FROM t tt WHERE t.str = tt.str);