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        while(l < r) {
            int mid = l+r>>1;
            if(a[mid] >= x) r = mid ;
            else l = mid + 1; 
        }
        if(a[l] != x) {
            cout<<"-1 -1"<<endl;
        }else {
            cout<<l-1<<" ";
            l = 1,  r= n ;
            while(l < r) {
                int mid = l+r+1>>1;
                if(a[mid] <= x) l = mid;
                else r = mid - 1; 
            }
            cout<<r-1<<endl;
        }