93.复原IP地址

class Solution {
public:vector<string> result;bool isValid(const string& s, int start, int end){if (start > end){return false;}if (s[start]=='0' && start != end){return false;}int num = 0;for (int i=start; i<=end; i++){if (s[i] > '9' || s[i]< '0'){ //非法字符return false;}num = num * 10 + (s[i] - '0');if (num > 255){ //如果大于255了不合法return false;}}return true;}void BackTracking(string& s, int startIndex, int pointNum){if (pointNum == 3){if (isValid(s, startIndex, s.size()-1)){result.push_back(s);}return ;}for (int i=startIndex; i<s.size(); i++){if (isValid(s, startIndex, i)){s.insert(s.begin()+i+1, '.'); //insertpointNum++;BackTracking(s, i+2, pointNum);pointNum--;s.erase(s.begin()+i+1);}else break; //不合法 直接结束循环}}vector<string> restoreIpAddresses(string s) {result.clear();if (s.size() < 4 || s.size()>12) return result;BackTracking(s, 0, 0);return result;}
};

78.子集

class Solution {
public:vector<vector<int>> result;vector<int> path;void BackTracking(vector<int>& nums, int index){result.push_back(path);if (index >= nums.size()){return ;}for (int i=index; i<nums.size(); i++){path.push_back(nums[i]);BackTracking(nums, i+1);path.pop_back();}}vector<vector<int>> subsets(vector<int>& nums) {result.clear();path.clear();BackTracking(nums, 0);return result;}
};

90.子集II

class Solution {
public:vector<vector<int>> result;vector<int> path;void BackTracking(vector<int>& nums, int index){result.push_back(path);if (index >= nums.size()){return ;}for (int i=index; i<nums.size(); i++){path.push_back(nums[i]);BackTracking(nums, i+1);path.pop_back();}}vector<vector<int>> subsets(vector<int>& nums) {result.clear();path.clear();sort(nums.begin(), nums.end());BackTracking(nums, 0);return result;}
};