算法训练营第二十四天|77.组合

Leetcode77.组合

文章链接：代码随想录
题目链接：77.组合

思路：正常的回溯思想，可以加上剪枝优化，思想在于剩余元素已经不够组成结果了就剪掉。
未剪枝：

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    void backtracking(int n, int k, int startIndex){
        if (path.size() == k){
            res.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 res;
    }
};

剪枝优化：

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

今天晚上闲着没事，先把明天的题刷了，挺简单哈哈
加油！！！