93.复原IP地址
题目链接：93.复原IP地址
文档链接：93.复原IP地址
视频链接：回溯算法如何分割字符串并判断是合法IP？| LeetCode：93.复原IP地址
C++实现
class Solution {
private: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] < '0' || s[i] > '9'){return false;}num = num * 10 + (s[i]-'0');if(num > 255){return false;}}return true;}void backtracking(string& s, int startIdx, int pointNum){if(pointNum == 3){if(isValid(s, startIdx, s.size()-1)){result.push_back(s); }return;}for(int i = startIdx; i<s.size();i++){if(isValid(s,startIdx, i)){s.insert(s.begin()+i+1,'.');pointNum++;backtracking(s, i+2, pointNum);pointNum--;s.erase(s.begin()+i+1);}else break;}return;}
public: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
题目链接：78.子集
文档链接：78.子集
视频链接：回溯算法解决子集问题，树上节点都是目标集和！ | LeetCode：78.子集
C++实现
class Solution {
private:vector<vector<int>> result;vector<int> path;void backtracking(vector<int>& nums, int startIdx){result.push_back(path);if(startIdx >= nums.size()) return;for(int i = startIdx; i<nums.size(); i++){path.push_back(nums[i]);backtracking(nums, i+1);path.pop_back();}return;}
public:vector<vector<int>> subsets(vector<int>& nums) {result.clear();path.clear();backtracking(nums, 0);return result;}
};
90.子集II
题目链接：90.子集II
文档链接：90.子集II
视频链接：回溯算法解决子集问题，如何去重？| LeetCode：90.子集II
C++实现
class Solution {
private:vector<vector<int>> result;vector<int> path;void backtracking(vector<int>& nums, int startIdx, vector<bool> used){result.push_back(path);if(startIdx>=nums.size()) return;for(int i = startIdx; i<nums.size(); i++){if(i>0 && nums[i]==nums[i-1] && used[i-1] == 0) continue;path.push_back(nums[i]);used[i] = true;backtracking(nums, i+1, used);used[i] = false;path.pop_back();}return;}public:vector<vector<int>> subsetsWithDup(vector<int>& nums) {result.clear();path.clear();sort(nums.begin(), nums.end());vector<bool> used(nums.size(), false);backtracking(nums, 0, used);return result;}
};
)
