Permutations

Given a collection of numbers, return all possible permutations. For example, [1,2,3] have the following permutations: [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1].

回溯，代码：

vector<vector<int> >& permute(vector<int> vecInt)
{
    vector<int> vecWorker;
    vector<vector<int> > vecPermu;
    helper(vecPermu, vecWorker, vecInt);

    return vecPermu;
}

void helper(vector<vector<int> >& vecPermu, vector<int>& vecWorker, const vector<int>& vecInt)
{
    if (vecWorker.size() == vecInt.size())
    {
        vecPermu.push_back(vecWorker);
        return;
    }

    for (int i = 0; i < vecInt.size(); i++)
    {
　　　　 // 这里用visited记录更好一些，参见 Permutations II
        if (find(vecWorker.begin(), vecWorker.end(), vecInt[i]) != vecWorker.end())
            continue;

        vecWorker.push_back(vecInt[i]);
        helper(vecPermu, vecWorker, vecInt);
        vecWorker.pop_back(vecInt[i]);
    }
}