回溯算法模版

https://leetcode-cn.com/problems/permutations/solution/pei-yang-chou-xiang-neng-li-de-yi-dao-ti-1731/

46. 全排列

List<List<Integer>> res = new LinkedList<>();
    public  List<List<Integer>> permute(int[] nums) {
        LinkedList<Integer> track = new LinkedList<>();
        backtrack(nums, track);
        return res;
    }

    void backtrack(int[] nums, LinkedList<Integer> track) {
        if (track.size() == nums.length) {
            LinkedList<Integer> ansPath = new LinkedList<>(track);
            res.add(ansPath);
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            //排除不合法的选择
            if (track.contains(nums[i])) {
                continue;
            }
            //做选择
            track.add(nums[i]);
            //进入下一层决策树
            backtrack(nums, track);
            //取消选择,或者回撤
            track.removeLast();
        }
    }

模版