/* Pseudocode */
MainCombination(para)
{
    /* return value */
    val;
    Check(para);
    BackTrack(val, initialCondition);
    return val;
}

BackTrack(val, initialCondition)
{
    /* terminal condition */
    if (isTerminal){
        val.add(initialCondition);
        return;
    }
    loop{
        /* proccess paras for next recursive */
        CurrentProccess(val, initialCondition);
        Dfs(val, initialCondition);
        TurnBackToLastStatus(val, initialCondition);
    }
}