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代码随想录算法训练营第37期第二十五天 | LeetCode216.组合总和III、17.电话号码的字母组合

一、216.组合总和III

解题代码C++：

class Solution {
private:
    vector<vector<int>> result;
    vector<int> path;
    void backtracing(int k, int n, int startIndex)
    {
        if(n < 0) return;
        
        if(n == 0 && path.size() == k)
        {
            result.push_back(path);
            return;
        }

        for(int i = startIndex; i <= 9; i ++)
        {
            path.push_back(i);
            backtracing(k, n - i, i + 1);
            path.pop_back();
        }
    }

public:
    vector<vector<int>> combinationSum3(int k, int n) {
        result.clear();
        path.clear();
        backtracing(k, n, 1);
        return result;
    }
};

题目链接/文章讲解/视频讲解：
https://programmercarl.com/0216.%E7%BB%84%E5%90%88%E6%80%BB%E5%92%8CIII.html

二、17.电话号码的字母组合

解题代码C++：

class Solution {
private:
    const string letterMap[10] = {
        "", //0
        "", //1
        "abc", //2
        "def", //3
        "ghi", //4
        "jkl", //5
        "mno", //6
        "pqrs", //7
        "tuv", //8
        "wxyz" //9
    };

public:
    vector<string> result;
    void getCombinations(const string& digits, int index, const string& s)
    {
        if(index == digits.size())
        {
            result.push_back(s);
            return;
        }

        int digit = digits[index] - '0';
        string letters = letterMap[digit];
        for(int i = 0; i < letters.size(); i ++)
            getCombinations(digits, index + 1, s + letters[i]);
    }

    vector<string> letterCombinations(string digits) {
        result.clear();
        if(digits.size() == 0)
            return result;
        getCombinations(digits, 0, "");
        return result;
    }
};