Permutation, swap, recursive

perm_swap_recursive.cpp

    void doPerm(vector<int>& nums, int start, 
                vector<vector<int>>& collector) {
        if (start == nums.size())
            collector.push_back(nums);
        else {
            for (int i = start; i < nums.size(); ++i) {
                std::swap(nums[start], nums[i]);
                doPerm(nums, start+1, collector);
                std::swap(nums[start], nums[i]);
            }
        }
    }