题解 | #没有重复项数字的全排列#

#include <vector>
struct pair_ {
    int i;
    bool used;
};
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param num int整型vector
     * @return int整型vector<vector<>>
     */

    void permute_(int pos, int len, vector<int>& num, vector<int>& res,
                  vector<vector<int> >& return_) {
        if (pos == len) {
            return_.push_back(res);
            return;
        }
        int target = num[pos];
        //首数字与之后的每个数字交换
        for (int i = pos; i < len; i++) {
            num[pos] = num[i];
            num[i] = target;
            res.push_back(num[pos]);
            permute_(pos + 1, len, num, res, return_);
            res.pop_back();
            num[i] = num[pos];
            num[pos] = target;
        }
    }

    vector<vector<int> > permute(vector<int>& num) {
        vector<vector<int> > return_;
        if (num.empty())
            return return_;
        vector<int> res;
        int len = num.size();
        permute_(0, len, num, res, return_);
        return return_;
    }
};