LeetCode 46.Permutations

题目：

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].

分析与解答：简单的递归dfs即可，注意不要重复了。

class Solution {
  public:
    vector<vector<int> > result;
    vector<vector<int> > permute(vector<int> &num) {
        vector<int> tempresult;//存放走过的路径
        dfs(num, tempresult);
        return result;
    }
    void dfs(vector<int> &num, vector<int> &tempresult) {
        if(tempresult.size() == num.size()) {
            result.push_back(tempresult);
            return;
        }
        for(int i = 0; i < num.size(); ++i) {
            auto index = find(tempresult.begin(), tempresult.end(), num[i]);
            if(index == tempresult.end()) { //没有重复过
                tempresult.push_back(num[i]);
                dfs(num, tempresult);
                tempresult.pop_back();
            }
        }
    }
};