LeetCode 77. combination

Title Description

77. Combine

solution

Regardless of efficiency , This problem is a typical problem that can be solved by backtracking framework , Details can be referred to LeetCode 78. A subset of

class Solution {
    
public:
    vector<vector<int>> res;
    vector<vector<int>> combine(int n, int k) {
    
        vector<int> track;
        backtrace(1, n, k, track);
        return res;
    }

    void backtrace(int start, int n, int k, vector<int>& track)
    {
    
        if (track.size() == k)
        {
    
            res.push_back(track);
            return;
        }
        for(int i = start; i <= n; i++)
        {
    
            track.push_back(i);
            backtrace(i + 1, n, k, track);
            track.pop_back();
        }
    }
};