代码随想录训练营第三十期|第二十七天|回溯算法part03|39. 组合总和● 40.组合总和II● 131.分割回文串

39. 组合总和 - 力扣（LeetCode）

class Solution {
    public List> combinationSum(int[] candidates, int target) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        dfs(res, list, candidates, target, 0, 0);
        return res;
    }

    private void dfs(List> res, List list, int[] candidates, int target, int sum, int idx) {
        if (sum > target) return;
        if (sum == target) {
            res.add(new ArrayList(list));
        }
        for (int i = idx; i < candidates.length; i++) {
            sum += candidates[i];
            list.add(candidates[i]);
            dfs(res, list, candidates, target, sum, i);
            sum -= candidates[i];
            list.remove(list.size() - 1);
        }
    }
}

40. 组合总和 II - 力扣（LeetCode）

class Solution {
    public List> combinationSum2(int[] candidates, int target) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        boolean[] visited = new boolean[candidates.length];
        Arrays.sort(candidates);
        dfs(res, list, candidates, target, visited, 0, 0);
        return res;
    }

    private void dfs(List> res, List list, int[] candidates, int target, boolean[] visited, int sum, int idx){
        if (sum > target) return;
        if (sum == target) {
            res.add(new ArrayList<>(list));
            return;
        }
        for (int i = idx; i < candidates.length; i++) {
            if (i > 0 && candidates[i] == candidates[i - 1] && !visited[i - 1]) continue;
            sum += candidates[i];
            visited[i] = true;
            list.add(candidates[i]);
            dfs(res, list, candidates, target, visited, sum, i + 1);
            sum -= candidates[i];
            visited[i] = false;
            list.remove(list.size() - 1);
        }
    }
}

131. 分割回文串 - 力扣（LeetCode）

class Solution {
    public List> partition(String s) {
        List> res = new ArrayList<>();
        List list = new ArrayList<>();
        dfs(res, list, s, 0);
        return res;
    }

    private void dfs(List> res, List list, String s, int idx) {
        if (idx >= s.length()) {
            res.add(new ArrayList<>(list));
            return;
        }

        for (int i = idx; i < s.length(); i++) {
            if (isPlindrom(s, idx, i)) {
                String sub = s.substring(idx, i + 1);
                list.add(sub);
            } else continue;
            dfs(res, list, s, i + 1);
            list.remove(list.size() - 1);
        }
    }

    private boolean isPlindrom(String s, int left, int right) {
        for (int i = left, j = right; i < j; i++, j--) {
            if (s.charAt(i) != s.charAt(j)) return false;
        }
        return true;
    }
}