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], and [3,2,1].

class Solution {
public:
    void visit(vector<int> &num, int size, int pos, vector<vector<int> > &result)
    {
        if (pos >= size)
        {
            result.push_back(num);
            return;
        }
        else
        {
            for (int i = pos; i < size; i++)
            {
                swap(num[pos], num[i]);
                visit(num, size, pos+1, result);
                swap(num[pos], num[i]);
            }
        }
    }
    
    vector<vector<int> > permute(vector<int> &num) {
        vector<vector<int> > result;

        int size = num.size();
        if (size < 1)
        {
            return result;
        }

        visit(num, size, 0, result);

        return result; 
    }
};