代码随想录算法训练营第二十七天 | 复原IP地址、子集,子集二

93.复原IP地址

class Solution {
public:
     vector<string> result;
    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 , '.');  
                pointNum++;
                backtracking(s, i + 2, pointNum);   
                pointNum--;                         
                s.erase(s.begin() + i + 1);        
            } else break; 
        }
    }
    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') { 
                return false;
            }
            num = num * 10 + (s[i] - '0');
            if (num > 255) { 
                return false;
            }
        }
        return true;
    }
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

class Solution {
public:
       vector<vector<int>> result;
        vector<int> path;
        void backtracking(vector<int>& nums, int startIndex) {
            result.push_back(path); 
            if (startIndex >= nums.size()) {
                return;
            }
            for (int i = startIndex; i < nums.size(); i++) {
                path.push_back(nums[i]);
                backtracking(nums, i + 1);
                path.pop_back();
            }
        }
    vector<vector<int>> subsets(vector<int>& nums) {
        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 startIndex, vector<bool>& used) {
        result.push_back(path);
        for (int i = startIndex; i < nums.size(); i++) {
            if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) {
                continue;
            }
            path.push_back(nums[i]);
            used[i] = true;
            backtracking(nums, i + 1, used);
            used[i] = false;
            path.pop_back();
        }
      }

    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        vector<bool> used(nums.size(), false);
        sort(nums.begin(), nums.end()); 
        backtracking(nums, 0, used);
        return result;
    }
};