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/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 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/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc:27:7: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
 gets(a);
       ^
In file included from /usr/include/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 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/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
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/cc2XwWdr.o: In function `main':
foo.cc:(.text.startup+0x3b): warning: the `gets' function is dangerous and should not be used.

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自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。