/usr/bin/ld: /tmp/ccIHfnMm.o: in function `query(int, int)':
grader.cpp:(.text+0x0): multiple definition of `query(int, int)'; /tmp/ccUepfcl.o:xylophone.cpp:(.text+0x0): first defined here
/usr/bin/ld: /tmp/ccIHfnMm.o: in function `answer(int, int)':
grader.cpp:(.text+0xa0): multiple definition of `answer(int, int)'; /tmp/ccUepfcl.o:xylophone.cpp:(.text+0xa0): first defined here
/usr/bin/ld: /tmp/ccIHfnMm.o: in function `main':
grader.cpp:(.text.startup+0x0): multiple definition of `main'; /tmp/ccUepfcl.o:xylophone.cpp:(.text.startup+0x0): first defined here
/usr/bin/ld: /tmp/ccUepfcl.o: in function `main':
xylophone.cpp:(.text.startup+0x84): undefined reference to `solve(int)'
/usr/bin/ld: /tmp/ccIHfnMm.o: in function `main':
grader.cpp:(.text.startup+0x30): undefined reference to `solve(int)'
collect2: error: ld returned 1 exit status