回溯第三天

93.复原IP地址

class Solution {
public:
    vector<string> result;
    bool isValid(string & s, int start, int end)
    {
        if(start > end)
            return false;
        if(s[start] == '0' && start != end)
            return false;
        int number = 0;
        for(int i = start; i <= end; i++)
        {
            if(s[i] < '0' ||s[i] > '9')
                return false;
            else
            {
                
                number = number * 10  + (s[i] - '0');
                if(number > 255)
                    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, '.');
                pointNum++;
                backTracking(s, i + 2, pointNum);
                pointNum--;
                s.erase(s.begin() + i + 1);
            }
            else
                break;
        }
    }
    vector<string> restoreIpAddresses(string s) {
        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> temp;
    void backTracking(vector<int> &nums, int startIndex)
    {
        if(startIndex > nums.size())
            return;
        for(int i = startIndex; i < nums.size(); i++)
        {
            temp.push_back(nums[i]);
            result.push_back(temp);
            backTracking(nums, i + 1);
            
            temp.pop_back();
           
            
        }

    }
    vector<vector<int>> subsets(vector<int>& nums) {
        result.push_back(temp);
        backTracking(nums, 0);
        
        return result;
    }
};

90. 子集 II

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

        }
    }
    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        vector<bool> isFollow(nums.size(), false);
        // result.push_back(temp);
        sort(nums.begin(), nums.end());
        backTracking(nums, 0, isFollow);
        return result;
    }
};