costs

/**
* Gets the cost of a node, the difference between neighbours from the opposite side and the current side
*
* @param int u  the node to calculate it's cost
*
* @returns int  the cost of a node
*
*/
int get_cost(int u, vi& neighbours, vi& neighbours_position, vi& sides){
    int side = sides[u];
    int cost = 0;

    for(int i = neighbours_position[u]; i < neighbours_position[u + 1]; ++i){
        if(side == sides[neighbours[i]]) --cost;
        else ++cost;
    }

    return cost;
}

/**
* Gets the cost of swapping two nodes in different sides, the difference between neighbours from the
* opposite side and the current side
*
* @param int u   the first node
* @param int v   the second node
*
* @returns int  the cost of swaping two nodes
*
*/
int get_cost(int u, int v, vi& neighbours, vi& neighbours_position, vi& sides){
    return get_cost(u, neighbours, neighbours_position, sides) + get_cost(v, neighbours, neighbours_position, sides) - 2;
}