day24 回溯3

93.复原IP地址

class Solution {
public:
    vector<string> res;
    string path;
    bool isValid(string s) {
        if (s.size() > 3 || (s.size() > 1 && s[0] == '0')) {
            return false;
        }
        if (stoi(s) > 255) {
            return false;
        }
        return true;
    }
    
    void backtracking(const string &s, int index) {
        if (index >= s.size() && path.size() == s.size() + 4) {
            res.push_back(path.substr(0, path.size() - 1));
            return;
        }
        for (int i = index; i < s.size(); i ++) {
            string str = s.substr(index, i - index + 1);
            if (isValid(str)) {
                path += str + ".";
                int n = str.size() + 1;
                backtracking(s, i + 1);
                while (n --) {
                    path.pop_back();
                }
            }
        }
    }

    vector<string> restoreIpAddresses(string s) {
        backtracking(s, 0);
        return res;
    }
};

78.子集

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    void backtracking(vector<int> &nums, int index) {
        res.push_back(path);
        if (index >= nums.size()) {
            return;
        }
        for (int i = index; 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 res;
    }
};

90.子集II

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    void backtracking(vector<int> &nums, int index) {
        res.push_back(path);
        if (index >= nums.size()) {
            return;
        }
        for (int i = index; i < nums.size(); i ++) {
            if (i > index && 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 res;
    }
};