int dpMinCostColor(vector<int>& a)
{
    int na=a.size();
    // 0: red, 1: blue, 2: green
    int costs[3][na];
    costs[0][0]=cr;
    costs[1][0]=cb;
    costs[2][0]=cg;

    for(int i=1;i<na;i++){
        costs[0][i]=cr + min(costs[1][i-1], costs[2][i-1]);
        costs[1][i]=cb + min(costs[0][i-1], costs[2][i-1]);
        costs[2][i]=cg + min(costs[0][i-1], costs[1][i-1]);
    }

    return min(costs[0][na-1], costs[1][na-1], costs[2][na-1]);
}