给定两个整数 n 和 k,返回 1 ... n 中所有可能的 k 个数的组合。
示例:
输入: n = 4, k = 2
输出:
[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]
C++
class Solution {
public:
void DFS(vector<vector<int>>& res, vector<int>& tmp, int n,int k, int w)
{
if(k==tmp.size())
{
res.push_back(tmp);
return;
}
for(int i=w;i<=n;i++)
{
if(tmp.size()<k)
{
tmp.push_back(i);
DFS(res,tmp,n,k,i+1);
tmp.pop_back();
}
}
}
vector<vector<int>> combine(int n, int k)
{
vector<vector<int>> res;
vector<int> tmp;
DFS(res,tmp,n,k,1);
return res;
}
};
python
class Solution:
def DFS(self, res, tmp, n, k, w):
if k==len(tmp):
res.append(tmp.copy())
return
for i in range(w,n+1):
if len(tmp)<k:
tmp.append(i)
self.DFS(res,tmp,n,k,i+1)
del tmp[-1]
def combine(self, n, k):
"""
:type n: int
:type k: int
:rtype: List[List[int]]
"""
res=[]
tmp=[]
self.DFS(res,tmp,n,k,1)
return res