算法修炼Day29|491.递增子序列 46.全排列 47.全排列 II

题目：491. 递增子序列 - 力扣（LeetCode）

代码实现：

class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    List<Integer> path = new ArrayList<>();
    public List<List<Integer>> findSubsequences(int[] nums) {
        backtracking(nums, 0);
        return ans;
    }
    private void backtracking(int[] nums, int startIndex) {
        if (path.size() > 1) {
            ans.add(new ArrayList<>(path));
        }
        HashSet<Integer> hs = new HashSet<>();
        for (int i = startIndex; 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]);
            backtracking(nums, i + 1);
            path.remove(path.size() - 1);
        }
    }
}

题目：46. 全排列 - 力扣（LeetCode）

代码实现：

class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    List<Integer> path = new ArrayList<>();
    boolean[] used;
    public List<List<Integer>> permute(int[] nums) {
        used = new boolean[nums.length];
        backtracking(nums);
        return ans;
    }
    private void backtracking(int[] nums) {
        if (path.size() == nums.length) {
            ans.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            if (used[i]) {
                continue;
            }
            used[i] = true;
            path.add(nums[i]);
            backtracking(nums);
            path.remove(path.size() - 1);
            used[i] = false;
        }
    }
}

题目：47. 全排列 II - 力扣（LeetCode）

代码实现：

class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    List<Integer> path = new ArrayList<>();
    public List<List<Integer>> permuteUnique(int[] nums) {
        boolean[] used = new boolean[nums.length];
        Arrays.sort(nums);
        backtracking(nums, used);
        return ans;
    }
    private void backtracking(int[] nums, boolean[] used) {
        if (path.size() == nums.length) {
            ans.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            if (i > 0 && nums[i - 1] == nums[i] && used[i - 1] == false) {
                continue;
            }
            if (used[i] == false) {
                path.add(nums[i]);
                used[i] = true;
                backtracking(nums, used);
                used[i] = false;
                path.remove(path.size() - 1);
            }
        }
    }
}