题目描述:
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],
]
解法:
class Solution {
public:
vector<vector<int>> combine(vector<int>& nums, int k){
vector<vector<int>> res;
int sz = nums.size();
if(k == 0){
return res;
}else if(k == 1){
for(int num : nums){
res.push_back({num});
}
return res;
}else if(k < sz){
int num = nums.back();
nums.pop_back();
res = combine(nums, k);
vector<vector<int>> tmp_res = combine(nums, k-1);
for(auto it : tmp_res){
it.push_back(num);
res.push_back(it);
}
nums.push_back(num);
return res;
}else if(k == sz){
return {nums};
}else{
return res;
}
}
vector<vector<int>> combine(int n, int k) {
vector<int> nums;
for(int i = 1; i <= n; i++){
nums.push_back(i);
}
return combine(nums, k);
}
};