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);}}
}