fn rollback(&mut self, time: usize) {
        let last = self.rollback_count(time);
        for _ in 0..last {
            self.votes.pop_front();
        }
    }
/// if a vote is expired, pop it and all the votes leading up to it
if a vote is expired, pop it and all the votes leading up to it
if a vote is expired pop it and all the votes leading up to it
fn rollback(&mut self, time: usize) {
        let last = self.rollback_count(time);
        for _ in 0..last {
            self.votes.pop_front();
        }
    }
fn rollback ( & mut self , time : usize ) { let last = self . rollback_count ( time ) ; for _ in 0 .. last { self . votes . pop_front ( ) ; } }
if a vote is expired, pop it and all the votes leading up to it
if a vote is expired pop it and all the votes leading up to it
&mut self
time
usize