93. 复原 IP 地址 - 力扣（LeetCode）

class Solution {
    ArrayList<String> results = new ArrayList<>();

    public List<String> restoreIpAddresses(String s) {
        if(s.length() > 12){
            return new ArrayList<>();
        }

        char[] ipChars = s.toCharArray();

        doRestoreIpAddresses(ipChars,0,"",4);

        return results;
    }

    public void doRestoreIpAddresses(char[] ipChars,int startPos,String oneResult,int remainCount){
        if(startPos == ipChars.length && remainCount == 0){
            results.add(oneResult.replaceFirst(".",""));
            return;
        }

        for(int i=startPos;i<ipChars.length;i++){
            if(remainCount < 0 || i-startPos >= 3){
                return;
            }

             //截取当前
            String nowSubString = new String(ipChars,startPos,i-startPos+1);
            if(Integer.parseInt(nowSubString) > 255 || (nowSubString.startsWith("0") && nowSubString.length()>=2)){
                return;
            }

            oneResult = oneResult + '.' + nowSubString;

            doRestoreIpAddresses(ipChars,i+1,oneResult,--remainCount);

            //不截取当前
            remainCount++;
            oneResult = oneResult.substring(0,oneResult.lastIndexOf("."));
        }
    }
}

78. 子集 - 力扣（LeetCode）

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        if(nums.length == 0){
            return new ArrayList<>();
        }

        ArrayList<Integer> oneResult = new ArrayList<>();
        ArrayList<List<Integer>> results = new ArrayList<>();

        doSubSets(nums,0,oneResult,results);

        return results;
    }

    private void doSubSets(int[] nums,int startPos,ArrayList<Integer> oneResult, List<List<Integer>> results){
        results.add(new ArrayList<>(oneResult));
        
        for(int i=startPos;i<nums.length;i++){
            oneResult.add(nums[i]);
            doSubSets(nums,i+1,oneResult,results);
            oneResult.remove(oneResult.size()-1);
        }
    }
}

90. 子集 II - 力扣（LeetCode）

class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        if(nums.length == 0){
            return new ArrayList<>();
        }

        Arrays.sort(nums);

        ArrayList<Integer> oneResult = new ArrayList<>();
        ArrayList<List<Integer>> results = new ArrayList<>();


        doSubsetsWithDup(nums,0,oneResult,results);
        
        return results;
    }

    public void doSubsetsWithDup(int[] nums,int startPos,ArrayList<Integer> oneResult,ArrayList<List<Integer>> results) {
        results.add(new ArrayList<>(oneResult));
        
        for(int i=startPos;i<nums.length;i++){
            if(i>startPos && nums[i] == nums[i-1]){
                continue;
            }
            
            oneResult.add(nums[i]);
            doSubsetsWithDup(nums,i+1,oneResult,results);
            oneResult.remove(oneResult.size()-1);
        }
    }
}