main.cpp

/// Source : https://leetcode.com/problems/permutations/description/
/// Author : liuyubobobo
/// Time   : 2017-11-18

#include <iostream>
#include <vector>
using namespace std;

/// Most Naive Recursive
/// Time Complexity: O(n^n)
/// Space Complexity: O(n)
class Solution {

private:

    vector<vector<int>> res;
    vector<bool> used;

    void generatePermutation(const vector<int>& nums, int index, vector<int>& p){

        if(index == nums.size()){
            res.push_back(p);
            return;
        }

        for(int i = 0 ; i < nums.size() ; i ++)
            if(!used[i]){
                used[i] = true;
                p.push_back(nums[i]);
                generatePermutation(nums, index + 1, p );
                p.pop_back();
                used[i] = false;
            }

        return;
    }

public:
    vector<vector<int>> permute(vector<int>& nums) {

        res.clear();
        if(nums.size() == 0)
            return res;

        used = vector<bool>(nums.size(), false);
        vector<int> p;
        generatePermutation(nums, 0, p);

        return res;
    }
};


void printVec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    int nums[] = {1, 2, 3};
    vector<int> vec(nums, nums + sizeof(nums)/sizeof(int) );

    vector<vector<int>> res = Solution().permute(vec);
    for(int i = 0 ; i < res.size() ; i ++)
        printVec(res[i]);

    return 0;
}