【Leetcode】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:
    vector<vector<int> > permute(vector<int> &num) {
        vector<vector<int> > result;
        sort(num.begin(), num.end());
        vector<int> path;
        dfs(num, path, result);
        return result;
    }
private:
    void dfs(vector<int> &num, vector<int> &path, vector<vector<int>> &result) {
        if (path.size() == num.size()) {
            result.push_back(path);
            return;
        }
        for (auto i : num) {
            if (find(path.begin(), path.end(), i) == path.end()) {
                path.push_back(i);
                dfs(num, path, result);
                path.pop_back();
            }
        } 
    }
};

可以利用next permutation的方法，一个一个求，也可以用dfs的方法来求所有的排列。上面的代码是dfs版。