全排列-回溯解法

回溯个人感觉和dfs加visited数组差不多，

public class Main{
    List<List<Integer>> res = new LinkedList<>();
    public List<List<Integer>> permute(int[] nums){
        LinkedList<Integer> track = new LinkedList<>();
        backTrack(track, nums);
        return res;
    }
    public void backTrack(LinkedList<Integer> track, int[] nums){
        if(track.size() == nums.length){
            res.add(new LinkedList(track));
            return;
        }

        for(int i=0; i<nums.length; ++i){
            if(track.contains(nums[i])) continue;
            track.add(nums[i]);
            backTrack(track, nums);
            track.removeLast();
        }
    }
    public static void main(String[] args) {
        Main m = new Main();
        m.test();


    }

    public void test(){
        permute(new int[]{1,2,3,4,5});
        for(List<Integer> list : res){
            for(Integer v : list){
                System.out.print(v+" ");
            }
            System.out.println();
        }
    }
}