代码随想录算法训练营第二十八天 | 93.复原IP地址

93.复原IP地址

题目链接 文章讲解 视频讲解

class Solution {
private:
    vector<string> ip;
    vector<string> result;
public:
    vector<string> restoreIpAddresses(string s) {
        backtracking(s, 0);
        return result;
    }

    void backtracking(const string& s, int startIndex) {
        if(startIndex == s.size()) {
            string res = "";
            int count = 0;
            for(int i = 0; i < ip.size(); ++i) {
                res += ip[i];
                if(i != ip.size() - 1) {
                    res += ".";
                    count++;
                }     
            } 
            if(count != 3) return ;
            result.push_back(res);
            return ;
        }

        for(int i = startIndex; i < s.size(); ++i) {
            if(isValid(s, startIndex, i)) {
                ip.push_back(s.substr(startIndex, i - startIndex + 1));
            } else continue;
            
            backtracking(s, i + 1);
            ip.pop_back();
        }

    }
    bool isValid(const string& s, int start, int end) {
        
        // 有前导0不合法
        if(s[start] == '0' && start != end) return false;

        // 如果不在0~255之间则不合法
        int dig = 0;
        for(int i = start; i <= end; ++i) {
            int num = s[i] - '0';
            dig = dig * 10 + num;
            if(dig < 0 || dig > 255) return false;
        }
        if(dig < 0 || dig > 255) return false;

        return true;
    }
};

78.子集

题目链接 文章讲解 视频讲解

关键：每一层递归都应收集结果

class Solution {
private:
    vector<int> sub;
    vector<vector<int>> result;
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        backtracking(nums, 0);
        return result;
    }

    void backtracking(vector<int>& nums, int startIndex) {
        result.push_back(sub);
        if(sub.size() == nums.size()) {
            return;
        }

        for(int i = startIndex; i < nums.size(); ++i) {
            sub.push_back(nums[i]);
            backtracking(nums, i + 1);
            sub.pop_back();
        }
    }
};

90.子集II

题目链接 文章讲解 视频讲解

class Solution {
private:
    vector<int> sub;
    vector<vector<int>> result;
public:
    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        backtracking(nums, 0);
        return result;
    }

    void backtracking(vector<int>& nums, int startIndex) {
        result.push_back(sub);

        for(int i = startIndex; i < nums.size(); ++i) {
            if(i > startIndex && nums[i] == nums[i - 1]) continue;
            sub.push_back(nums[i]);
            backtracking(nums, i + 1);
            sub.pop_back();
        }
    }
};