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()));    }}