代码随想录算法训练营第二十九天| 491.递增子序列、46.全排列、47.全排列 II

491.递增子序列

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

解题思路：同层相同元素要跳过

java：

class Solution {
    List> result=new ArrayList<>();
    List path=new ArrayList<>();
    public List> findSubsequences(int[] nums) {
        backTrace(nums,0);
        return result;
    }
    public void backTrace(int[] nums,int start){
        if(path.size()>1)
            result.add(new ArrayList(path));
        HashSet hs = new HashSet<>();
        for(int i = start; i < nums.length; i++){
            if(!path.isEmpty() && path.get(path.size() -1 ) > nums[i] || hs.contains(nums[i]))
                continue;
            hs.add(nums[i]);
            path.add(nums[i]);
            backTrace(nums, i + 1);
            path.remove(path.size() - 1);
        }
    }
}

46.全排列

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

解题思路：只需要将每轮第一个访问跳过

java：

class Solution {
    List> result = new ArrayList<>();
    LinkedList path = new LinkedList<>();
    boolean[] used;
    public List> permute(int[] nums) {
        if (nums.length == 0){
            return result;
        }
        used = new boolean[nums.length];
        permuteHelper(nums);
        return result;
    }
    private void permuteHelper(int[] nums){
        if (path.size() == nums.length){
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < nums.length; i++){
            if (used[i]){
                continue;
            }
            used[i] = true;
            path.add(nums[i]);
            permuteHelper(nums);
            path.removeLast();
            used[i] = false;
        }
    }
}

47.全排列 II

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

解题思路：同层的跳过

java：

class Solution {
    List> result = new ArrayList<>();
    LinkedList path = new LinkedList<>();
    boolean[] used;
    public List> permuteUnique(int[] nums) {
        if (nums.length == 0){
            return result;
        }
        used = new boolean[nums.length];
        permuteHelper(nums);
        return result;
    }
    private void permuteHelper(int[] nums){
        if (path.size() == nums.length){
            result.add(new ArrayList<>(path));
            return;
        }
        HashSet hs=new HashSet<>();
        for (int i = 0; i < nums.length; i++){
            if (used[i]||hs.contains(nums[i])){
                continue;
            }
            used[i] = true;
            hs.add(nums[i]);
            path.add(nums[i]);
            permuteHelper(nums);
            path.removeLast();
            used[i] = false;
        }
    }
}