代码随想录算法训练营第二十八天| 93.复原IP地址、78.子集、90.子集II

93.复原IP地址

题目链接
文章讲解

class Solution {
public:
    vector<string> ans;

    bool isVaild(const string& s, const int& begin, const int& end) {
        if (begin > end) return false;
        if (s[begin] == '0' && begin != end) return false;
        int sum = 0;
        for (int i = begin; i <= end; i++) {
            sum = sum * 10 + s[i] - '0';
            if (sum > 255) return false;
        }
        return true;
    }

    void backtracking(string& s, int idx, int pointNum) {
        if (pointNum == 3) {
            if (isVaild(s, idx, s.size() - 1))
                ans.push_back(s);
            return;
        }
        for (int i = idx; i < s.size() && isVaild(s, idx, i); i++) {
            s.insert(s.begin() + i + 1, '.');
            backtracking(s, i + 2, pointNum + 1);
            s.erase(s.begin() + i + 1);
        }
    }

    vector<string> restoreIpAddresses(string s) {
        if (s.size() < 4 || s.size() > 12) return ans;
        backtracking(s, 0, 0);
        return ans;
    }
};

78.子集

题目链接
文章讲解

class Solution {
public:
    vector<vector<int>> ans = {{}};
    vector<int> path;

    void backtracking(const vector<int>& nums, int start) {
        for (int i = start; i < nums.size(); i++) {
            path.push_back(nums[i]);
            ans.push_back(path);
            if (i + 1 < nums.size()) backtracking(nums, i + 1);
            path.pop_back();
        }
    }

    vector<vector<int>> subsets(vector<int>& nums) {
        backtracking(nums, 0);
        return ans;
    }
};

90.子集II

题目链接
文章讲解

class Solution {
public:
    vector<int> path;
    vector<vector<int>> ans;

    void backtracking(const vector<int>& nums, int start) {
        ans.push_back(path);
        for (int i = start; i < nums.size(); i++) {
            if (i > start && nums[i] == nums[i - 1]) continue;
            path.push_back(nums[i]);
            backtracking(nums, i + 1);
            path.pop_back();
        }
    }

    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        backtracking(nums, 0);
        return ans;
    }
};