Paint House!

• Time : $O(n)$
• Space : $O(1)$

int Solution::solve(vector<vector<int> > &A) {
    int r = 0, g = 0, b = 0;
    for(auto a : A) {
        int rr = min(g,b) + a[0];
        int gg = min(r,b) + a[1];
        int bb = min(r,g) + a[2];
        r = rr;
        g = gg;
        b = bb;
    }
    
    return min({r,g,b});
}