Algorithm 2: Anonymous Query Set Generation Algorithm

Input: k, Z′, S, R, Local cache location dataset O, User’s current location loc Output: Anonymous location set Z 1: Z = $\varnothing$; 2: if length(Z′) ≥ k − 1 3:         sort points in Z′ by predicted probability; 4:         return Z = the first k − 1 points in Z′ + {loc + Lap(εi)}; 5: else 6:         Z = Z′; 7:         S′ = points in S that are in the range R; 8:         sort points in S′ by query probability; 9:         i = 0; 10:       while length(Z) < k − 1 do 11:                 if S′[i] is not in Z and S′[i] is not in O 12:                         Z + = S′[i]; 13:                         if length(Z) == k − 1 14:                                 break; 15:                 i + + ; 16:       return Z = Z + {loc + Lap(εi)};