foo.cc: In function 'bool go()':
foo.cc:13:18: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
 if (a[i] == a[j] && a[p] == a[q] || a[i] == a[q] && a[p] == a[j])
     ~~~~~~~~~~~~~^~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:25:7: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
 gets(a);
       ^
In file included from /usr/include/c++/7/cstdio:42:0,
                 from /usr/include/c++/7/ext/string_conversions.h:43,
                 from /usr/include/c++/7/bits/basic_string.h:6361,
                 from /usr/include/c++/7/string:52,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:27:7: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
 gets(a); 
       ^
In file included from /usr/include/c++/7/cstdio:42:0,
                 from /usr/include/c++/7/ext/string_conversions.h:43,
                 from /usr/include/c++/7/bits/basic_string.h:6361,
                 from /usr/include/c++/7/string:52,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from foo.cc:1:
/usr/include/stdio.h:638:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.cc:25:5: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
 gets(a);
 ~~~~^~~
foo.cc:27:5: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
 gets(a); 
 ~~~~^~~
/tmp/ccbW9WF8.o: In function `main':
foo.cc:(.text.startup+0x2a): warning: the `gets' function is dangerous and should not be used.

自豪的采用 HydroJudger 进行评测(github.com/hydro-dev/HydroJudger)

{"receive":"2020-05-27T13:56:36.683Z","handle":"2020-05-27T13:56:36.683Z","cache_start":"2020-05-27T13:56:36.690Z","read_cases":"2020-05-27T13:56:37.267Z","judge":"2020-05-27T13:56:37.267Z","done":"2020-05-27T13:56:37.815Z"}