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

 491.递增子序列  Non-decreasing Subsequences - LeetCode

 二维 res

一维 path

void backtracking(nums, startIndex)

        if (path.size() > 1) res.add(path);

        Set used ;//记录

        for (int i = startIndex; i < nums.length; i++)

                if（!path.size().isEmpaty()&& nums[i] < path.back && set.contains[i]) continue;

                used.add(nums[i]);

                path.add(nums[i]);

                backtracking(nums, i + 1);

                path.remove(path.size() - 1);

           

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

    private void backtracking(List> res, List path, int[] nums, int startIndex) {
        if (path.size() > 1) {
            res.add(new ArrayList<>(path));
        }
        Set set = new HashSet<>();
        for (int i = startIndex; i < nums.length; i++) {
            if (!path.isEmpty() && path.get(path.size() - 1) > nums[i] || set.contains(nums[i])) continue;
            set.add(nums[i]);
            path.add(nums[i]);
            backtracking(res, path, nums, i + 1);
            path.remove(path.size() - 1);
        }
    }
}

    

* 46.全排列 Permutations - LeetCode

二维 res

一维 path

void backtracking(nums, used,)

        if (path.size == nums.length)

                res.add(path);

                return;

for (int i = 0; i < nums.size(); i++)

        if (used[i] == true) continue;

        path.add(nums[i]);

        backtracking(nums, used)

        used[i] = false;

        path.remove(path.size() - 1);

class Solution {
    public List> permute(int[] nums) {
        List> res = new ArrayList<>();
        List path = new ArrayList<>();
        boolean[] used = new boolean[nums.length];
        backtracking(res, path, nums, used);
        return res;
    }

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

        for (int i = 0; i < nums.length; i++) {
            if (used[i]) continue;
            path.add(nums[i]);
            used[i] = true;
            backtracking(res, path, nums, used);
            path.remove(path.size() - 1);
            used[i] = false;
        }
    }


}

* 47.全排列 II Permutations II - LeetCode

二维 res

一维 path

Arrays.sort(nums);

void backtracking(nums, used)

        if (path.size() == nums.length)

                res.add(path);

                return;

        for (int i = 0; i < nums.length; i++)

                if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] = false) continue;

                if (used[i] == true) continue;

                path.add（nums[i]);

                used[i] = true;

                backtracking(nums, used);

                path.remove(path.size() - 1);

                used[i] = false;

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

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