代码随想录 Day29 - 回溯（五）

package jjn.carl.backtrack;
import java.util.*;
/**
 * @author Jjn
 * @since 2023/7/29 13:26
 */
public class LeetCode491 {
    public List<List<Integer>> findSubsequences(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        backtrack(nums, result, 0, new ArrayList<>());
        return result;
    }
    private void backtrack(int[] nums, List<List<Integer>> result, int startIndex, List<Integer> path) {
        if (path.size() >= 2) {
            result.add(new ArrayList<>(path));
        }
        Set<Integer> set = new HashSet<>();
        for (int i = startIndex; i < nums.length; i++) {
            if (!path.isEmpty() && nums[i] < path.get(path.size() - 1) || set.contains(nums[i])) {
                continue;
            }
            path.add(nums[i]);
            set.add(nums[i]);
            backtrack(nums, result, i + 1, path);
            path.remove(path.size() - 1);
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int totalNumber = scanner.nextInt();
        int[] nums = new int[totalNumber];
        for (int i = 0; i < totalNumber; i++) {
            nums[i] = scanner.nextInt();
        }
        List<List<Integer>> subsequences = new LeetCode491().findSubsequences(nums);
        System.out.println(String.join(",", subsequences.toString()));
    }
}

package jjn.carl.backtrack;
import ljl.alg.wangzheng_camp.round1.tree._offer34_path_sum;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jjn
 * @since 2023/7/29 14:02
 */
public class LeetCode46 {
    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        boolean[] used = new boolean[nums.length];
        backtrack(nums, 0, new ArrayList<>(), result, used);
        return result;
    }
    private void backtrack(int[] nums, int startIndex, List<Integer> path, List<List<Integer>> result, boolean[] used) {
        if (startIndex == nums.length) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            if (used[i]) {
                continue;
            }
            path.add(nums[i]);
            used[i] = true;
            backtrack(nums, startIndex + 1, path, result, used);
            path.remove(path.size() - 1);
            used[i] = false;
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int total = scanner.nextInt();
        int[] nums = new int[total];
        for (int i = 0; i < total; i++) {
            nums[i] = scanner.nextInt();
        }
        List<List<Integer>> list = new LeetCode46().permute(nums);
        System.out.println(String.join(",", list.toString()));
    }
}

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jjn
 * @since 2023/7/29 14:11
 */
public class LeetCode47 {
    public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums);
        boolean[] used = new boolean[nums.length];
        backtrack(nums, new ArrayList<>(), result, used);
        return result;
    }
    private void backtrack(int[] nums, List<Integer> path, List<List<Integer>> result, boolean[] used) {
        if (path.size() == nums.length) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = 0; i < nums.length; i++) {
            if (i > 0 && nums[i] == nums[i - 1] && !used[i - 1]) {
                continue;
            }
            if (!used[i]) {
                path.add(nums[i]);
                used[i] = true;
                backtrack(nums, path, result, used);
                used[i] = false;
                path.remove(path.size() - 1);
            }
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int total = scanner.nextInt();
        int[] nums = new int[total];
        for (int i = 0; i < total; i++) {
            nums[i] = scanner.nextInt();
        }
        List<List<Integer>> lists = new LeetCode47().permuteUnique(nums);
        System.out.println(String.join(",", lists.toString()));
    }
}