代码随想录 Day27 - 回溯（三）

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
/**
 * @author Jjn
 * @since 2023/7/24 10:14
 */
public class LeetCode39 {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        Arrays.sort(candidates);
        List<List<Integer>> result = new ArrayList<>();
        if (candidates.length == 0) {
            return result;
        }
        backtrack(target, result, new ArrayList<>(), 0, candidates, 0);
        return result;
    }
    private void backtrack(int target, List<List<Integer>> result, List<Integer> path, int sum, int[] candidates, int startIndex) {
        if (sum > target) {
            return;
        }
        if (sum == target) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = startIndex; i < candidates.length; i++) {
            if (sum + candidates[i] > target) {
                break;
            }
            path.add(candidates[i]);
            backtrack(target, result, path, sum + candidates[i], candidates, i);
            path.remove(path.size() - 1);
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int candidateNum = scanner.nextInt();
        int target = scanner.nextInt();
        int[] candidates = new int[candidateNum];
        for (int i = 0; i < candidateNum; i++) {
            candidates[i] = scanner.nextInt();
        }
        List<List<Integer>> lists = new LeetCode39().combinationSum(candidates, target);
        System.out.println(String.join(",", lists.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 2023-07-24 23:43
 */
public class LeetCode40 {
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        Arrays.sort(candidates);
        boolean[] used = new boolean[candidates.length];
        List<List<Integer>> result = new ArrayList<>();
        backtrack(candidates, target, 0, 0, result, new ArrayList<>(), used);
        return result;
    }
    private void backtrack(int[] candidates, int target, int sum, int startIndex, List<List<Integer>> result,
                           List<Integer> path, boolean[] used) {
        if (sum > target) {
            return;
        }
        if (sum == target) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = startIndex; i < candidates.length; i++) {
            if (i >= 1 && candidates[i] == candidates[i - 1] && !used[i - 1]) {
                continue;
            }
            path.add(candidates[i]);
            used[i] = true;
            backtrack(candidates, target, sum + candidates[i], i + 1, result, path, used);
            path.remove(path.size() - 1);
            used[i] = false;
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int totalNum = scanner.nextInt();
        int target = scanner.nextInt();
        int[] candidates = new int[totalNum];
        for (int i = 0; i < totalNum; i++) {
            candidates[i] = scanner.nextInt();
        }
        List<List<Integer>> list = new LeetCode40().combinationSum2(candidates, target);
        System.out.println(String.join(",", list.toString()));
    }
}

package jjn.carl.backtrack;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Scanner;
/**
 * @author Jjn
 * @since 2023/7/25 22:56
 */
public class LeetCode131 {
    public List<List<String>> partition(String s) {
        List<List<String>> result = new ArrayList<>();
        backtrack(s, 0, new ArrayList<>(), result);
        return result;
    }
    private void backtrack(String s, int startIndex, List<String> path, List<List<String>> result) {
        if (startIndex >= s.length()) {
            result.add(new ArrayList<>(path));
            return;
        }
        for (int i = startIndex; i < s.length(); i++) {
            if (!isPalindrome(s.substring(startIndex, i + 1))) {
                continue;
            }
            path.add(s.substring(startIndex, i + 1));
            backtrack(s, i + 1, path, result);
            path.remove(path.size() - 1);
        }
    }
    private boolean isPalindrome(String s) {
        if (s == null || s.length() <= 1) {
            return true;
        }
        int left = 0, right = s.length() - 1;
        while (left < right) {
            if (!Objects.equals(s.charAt(left), s.charAt(right))) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();
        List<List<String>> partition = new LeetCode131().partition(input);
        System.out.println(String.join(",", partition.toString()));
    }
}