Compactando tuplas (pontos 2D, 3D)

typedef pair<int, int> ii;
map<ii, int> PD;
map<ii, int>::iterator PDi;
...
int funcao(int a, int b) {
    ...
    PDi = PD.find(ii(a, b));
    if (PDi != PD.end())
        return PDi->second;
    ...
    return PD[ii(a, b)] = resp;
}