代码随想录训练营第三十期|第二十九天|回溯算法part05|491.递增子序列* 46.全排列* 47.全排列 II

491. 非递减子序列 - 力扣（LeetCode）

class Solution {
    public List> findSubsequences(int[] nums) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        dfs(res, list, nums, 0);
        return res;
    }

    private void dfs(List> res, List list, int[] nums, int idx) {
        if (list.size() >= 2) {
            res.add(new ArrayList<>(list));
        }

        Map map = new HashMap<>();
        for (int i = idx; i < nums.length; i++) {
            if (!list.isEmpty() && list.get(list.size() - 1) > nums[i]) continue;
            if (map.getOrDefault(nums[i], 0) >= 1) continue;
            map.put(nums[i], map.getOrDefault(nums[i], 0) + 1);
            list.add(nums[i]);
            dfs(res, list, nums, i + 1);
            list.remove(list.size() - 1);
        }
    }
}

46. 全排列 - 力扣（LeetCode）

class Solution {
    public List> permute(int[] nums) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        dfs(res, list, nums);
        return res;
    }

    private void dfs(List> res, List list, int[] nums) {
        if (list.size() == nums.length) {
            res.add(new ArrayList<>(list));
            return;
        }

        for (int i = 0; i < nums.length; i++) {
            if (list.contains(nums[i])) continue;
            list.add(nums[i]);
            dfs(res, list, nums);
            list.remove(list.size() - 1);
        }
    }
}

47. 全排列 II - 力扣（LeetCode）

class Solution {
    public List> permuteUnique(int[] nums) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        Arrays.sort(nums);
        boolean[] visited = new boolean[nums.length];
        dfs(res, list, nums, visited);
        return res;
    }

    private void dfs(List> res, List list, int[] nums, boolean[] visited) {       
        if (list.size() == nums.length) {
            res.add(new ArrayList<>(list));
            return;
        }
        for(int i = 0; i < nums.length; i++) {
            if (visited[i]) continue;
            if (i > 0 && nums[i] == nums[i - 1] && !visited[i - 1]) continue;
            visited[i] = true;
            list.add(nums[i]);
            dfs(res, list, nums, visited);
            list.remove(list.size() - 1);
            visited[i] = false;

        }
    }
}