排列组合Leetcode Combinations

n个数取k个的集合

自己写的代码：

class Solution {
public:
    vector<int>v1;
    vector<vector<int>>v;
    vector<vector<int>> combine(int n, int k) {
        v.clear();    
        vector<int>exist(n,0);
        add(exist,n,k,0);
        return v;
    }
    void add(vector<int>&exist,int n,int k,int cur)
    { 
        if(cur<n)
        {
         exist[cur]=1;
         add(exist,n,k,cur+1);
         exist[cur]=0;
         add(exist,n,k,cur+1);
        }
        if(cur==n&&count(exist.begin(),exist.end(),1)==k)
        {
            v1.clear();
            for(int i=0;i<n;i++)
            {
                if(exist[i]==1)
                v1.push_back(i+1);
            }   
            v.push_back(v1);
            //return;
        }      
    }
};

 参考代码

class Solution {
 private:
     vector<vector<int> > ret;
     vector<int> a;
 public:
     void solve(int dep, int maxDep, int n, int start)
     {
         if (dep == maxDep)
         {
             ret.push_back(a);
             return;
         }      
         for(int i = start; i <= n; i++)
         {
             a[dep] = i;
             solve(dep + 1, maxDep, n, i + 1);
         }      
     }   
     vector<vector<int> > combine(int n, int k) {
         a.resize(k);
         ret.clear();
         solve(0, k, n, 1);
         return ret;
     }
 };