foo.cc: In function 'int main()':
foo.cc:40:14: warning: suggest parentheses around comparison in operand of '^' [-Wparentheses]
    if (i ^ j != 0) f[i] += f[j];
            ~~^~~~

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