day23|39. 组合总和,40.组合总和II ,131.分割回文串

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#算法

39. 组合总和

39. 组合总和 - 力扣（LeetCode）

class Solution {
public:
    vector<vector<int>> ans;
    vector<int> path;
    void combinationSum(vector<int>& candidates, int begin, int target, int& sum){
        if(sum > target){
            return ;
        }
        if(sum == target){
            ans.push_back(path);
            return ;
        }
        for(int i = begin; i < candidates.size(); i++){
            path.push_back(candidates[i]);
            sum += candidates[i];
            combinationSum(candidates, i, target, sum);
            path.pop_back();
            sum -= candidates[i];
        }
    }
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        int sum = 0;
        combinationSum(candidates, 0, target, sum);
        return ans;
    }
};

40.组合总和II

40. 组合总和 II - 力扣（LeetCode）

class Solution {
public:
    vector<vector<int>> ans;
    vector<int> path;
    void combinationSum(vector<int>& candidates, int begin, int target, int& sum){
        if(sum > target){
            return ;
        }
        if(sum == target){
            ans.push_back(path);
            return ;
        }
        for(int i = begin; i < candidates.size(); i++){
            path.push_back(candidates[i]);
            sum += candidates[i];
            combinationSum(candidates, i + 1, target, sum);
            path.pop_back();
            sum -= candidates[i];
            while(i < candidates.size()- 1 && candidates[i] == candidates[i + 1]){
                i++;  
            }// 相同位置不能放相同数字
        }
    }
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        int sum = 0;
        sort(candidates.begin(), candidates.end());   // 排序将相同数放在一起
        combinationSum(candidates, 0, target, sum);
        return ans;
    }
};

131.分割回文串

131. 分割回文串 - 力扣（LeetCode）

class Solution {
public:
    vector<vector<string>> result;
    string path;  // 记录单个字符串
    bool palindrome(string s){
        int left = 0, right = s.size() - 1;
        while(left < right){
            if(s[left++] != s[right--]){
                return false;
            }
        }
        return true;
    }   
    void partition(string s, int begin, vector<string> paths, int pathsLen){
        string path;
        if(pathsLen == s.size()){
            result.push_back(paths);
            return ;
        }
        for(int i = begin; i < s.size(); i++){
            path += s[i];
            if(palindrome(path)){
                paths.push_back(path);
                pathsLen += path.size();
                partition(s, i + 1, paths, pathsLen);
                paths.pop_back();
                pathsLen -= path.size();
            }
        }
    }
    vector<vector<string>> partition(string s) {
        vector<string> paths;
        partition(s, 0, paths, 0);
        return result;
    }
};