代码随想录 Day28 - 回溯（四）

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jjn
 * @since 2023/7/29 10:49
 */
public class LeetCode93 {
    public List<String> restoreIpAddresses(String s) {
        List<String> result = new ArrayList<>();
        if (s.length() > 12 || s.length() < 4) {
            return result;
        }
        backtrack(s, result, 0, 4, new ArrayList<>());
        return result;
    }
    private void backtrack(String s, List<String> result, int startIndex, int pointNum, List<String> parts) {
        if (startIndex == s.length()) {
            if (pointNum == 0) {
                result.add(String.join(".", parts));
                return;
            }
        }
        for (int i = startIndex; i < startIndex + 3; i++) {
            if (i >= s.length()) {
                break;
            }
            if (s.length() - i > pointNum * 3) {
                continue;
            }
            if (isValidPart(s, startIndex, i)) {
                parts.add(s.substring(startIndex, i + 1));
                backtrack(s, result, i + 1, pointNum - 1, parts);
                parts.remove(parts.size() - 1);
            }
        }
    }
    private boolean isValidPart(String s, int start, int end) {
        if (s == null || s.isEmpty()) {
            return false;
        }
        int subLength = end - start + 1;
        if (subLength > 3) {
            return false;
        }
        if (subLength > 1) {
            if (s.charAt(start) == '0') {
                return false;
            }
        }
        int sum = 0;
        for (int i = start; i <= end; i++) {
            int ithChar = s.charAt(i) - '0';
            sum = 10 * sum + ithChar;
        }
        return sum >= 0 && sum <= 255;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.nextLine();
        List<String> addresses = new LeetCode93().restoreIpAddresses(s);
        System.out.println(addresses.toString());
    }
}

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jiang Jining
 * @since 2023-07-26 23:14
 */
public class LeetCode78 {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        backtrack(nums, 0, new ArrayList<>(), result);
        return result;
    }
    private void backtrack(int[] nums, int startIndex, List<Integer> path, List<List<Integer>> result) {
        result.add(new ArrayList<>(path));
        for (int i = startIndex; i < nums.length; i++) {
            path.add(nums[i]);
            backtrack(nums, i + 1, path, result);
            path.remove(path.size() - 1);
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();
        int[] nums = new int[count];
        for (int i = 0; i < count; i++) {
            nums[i] = scanner.nextInt();
        }
        List<List<Integer>> subsets = new LeetCode78().subsets(nums);
        System.out.println(String.join(",", subsets.toString()));
    }
}

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jiang Jining
 * @since 2023-07-26 23:32
 */
public class LeetCode90 {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        Arrays.sort(nums);
        List<List<Integer>> result = new ArrayList<>();
        boolean[] used = new boolean[nums.length];
        backtrack(result, nums, 0, new ArrayList<>(), used);
        return result;
    }
    private void backtrack(List<List<Integer>> result, int[] nums, int startIndex, List<Integer> path, boolean[] used) {
        result.add(new ArrayList<>(path));
        for (int i = startIndex; i < nums.length; i++) {
            if (i >= 1 && nums[i] == nums[i - 1] && !used[i - 1]) {
                continue;
            }
            path.add(nums[i]);
            used[i] = true;
            backtrack(result, nums, i + 1, path, used);
            path.remove(path.size() - 1);
            used[i] = false;
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();
        int[] nums = new int[count];
        for (int i = 0; i < count; i++) {
            nums[i] = scanner.nextInt();
        }
        List<List<Integer>> lists = new LeetCode90().subsetsWithDup(nums);
        System.out.println(String.join(",", lists.toString()));
    }
}