foo.cc: In function 'int main()':
foo.cc:14:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
         if(a>=11&&a-b>=2||b>=11&&b-a>=2) {cout<<a<<':'<<b<<endl;a=0;b=0;}
            ~~~~~^~~~~~~~
foo.cc:22:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
         if(a>=21&&a-b>=2||b>=21&&b-a>=2) {cout<<a<<':'<<b<<endl;a=0;b=0;}
            ~~~~~^~~~~~~~

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