I was trying to solve this problem. With this code I got several WA & wasted hours of time by debugging it. But I've changed to this got AC! With no change of idea. All I changed was a line of code O_o.

it = lower_bound( v.begin() , v.end() , com [ i ].size() );

to

a = com [ i ].size();

it = lower_bound( v.begin() , v.end() , a );

Is there any problem with that?

Thank You.