public int getMax(int start,int end){
            if(this.start == start && this.end == end) return maxVal;
            int mid = (this.start + this.end)/2;
            if(start <= mid && end <= mid) return left.getMax(start,end);
            if(start > mid && end > mid) return right.getMax(start,end);
            return Math.max(left.getMax(start,mid),right.getMax(mid+1,end));
        }