【LC刷题】DAY19：77 216 17

最新推荐文章于 2024-07-01 00:46:53 发布

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【LC刷题】DAY19：77 216 17

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【LC刷题】DAY19：77 216 17

77. 组合 link

class Solution {
public:
    vector<vector<int>> result;
    vector<int> path;
    void backtracking(int n, int k, int startIndex){
        if(path.size() == k){
            result.push_back(path);
            return;
        }
        for(int i = startIndex; i <= n; i ++ ){
            path.push_back(i);
            backtracking(n, k, i + 1);
            path.pop_back();
        }
    }
    vector<vector<int>> combine(int n, int k) {
        backtracking(n, k, 1);
        return result;
    }
};

216. 组合总和 III link

class Solution {
public:
    vector<vector<int>> result;
    vector<int> path;
    void backtracking(int targetSum, int k, int sum, int startIndex){
        if(path.size() == k){
            if(sum == targetSum)
                result.push_back(path);
            return;
        }
        for(int i = startIndex; i <= 9; i ++){
            sum += i;
            path.push_back(i);
            backtracking(targetSum, k, sum, i + 1);
            sum -= i;
            path.pop_back();
        }
    }
    vector<vector<int>> combinationSum3(int k, int n) {
        backtracking(n, k, 0, 1);
        return result;
    }
};

17. 电话号码的字母组合link

class Solution {
public:
    const string letterMap[10] = {
        "", // 0
        "", // 1
        "abc", // 2
        "def", // 3
        "ghi", // 4
        "jkl", // 5
        "mno", // 6
        "pqrs", // 7
        "tuv", // 8
        "wxyz", // 9
    };
    vector<string> result;
    string s;
    void backtracking(const string& digits, int index){
        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 ++){
            s.push_back(letters[i]);
            backtracking(digits, index + 1);
            s.pop_back();
        }
    }
    vector<string> letterCombinations(string digits) {
        if(digits.size() == 0){
            return result;
        }

        backtracking(digits, 0);
        return result;
    }
};