46.排列的所有可能组合

Permutations

问题描述：

Given a collection of distinct 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]
]

参考答案：

class Solution {public:    vector<vector<int> > permute(vector<int> &num) {        vector<vector<int> > result;        permuteRecursive(num, 0, result);        return result;    }    // permute num[begin..end]    // invariant: num[0..begin-1] have been fixed/permuted    void permuteRecursive(vector<int> &num, int begin, vector<vector<int> > &result)    {        if (begin >= num.size()) {            // one permutation instance            result.push_back(num);            return;        }        for (int i = begin; i < num.size(); i++) {            swap(num[begin], num[i]);            permuteRecursive(num, begin + 1, result);            // reset            swap(num[begin], num[i]);        }    }};

性能：