8.5—暴力枚举法—Combinations

描述
Given two integers n and k, return all possible combinations of k numbers out of 1...n.
For example, If n = 4 and k = 2, a solution is:
[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]

#include<iostream>#include<algorithm>#include<vector>using namespace std;bool comp(const vector<int> &a, const vector<int> &b){return a.size() < b.size();}vector<vector<int>> Subsets(vector<int> data){vector<vector<int>> result;if (data.size() <= 0)return result;int length = data.size();int num = pow(2, length);int num1 = pow(2, length - 1);sort(data.begin(), data.end());for (int i = 0; i < num; i++){vector<int> path;if (i == 0){result.push_back(path);continue;}for (int j = 0; j < length; j++){int temp = num1;temp = temp >>= j;if (i&temp){path.push_back(data[j]);}}result.push_back(path);}return result;}vector<vector<int>>Combination(vector<int>data,int k){vector<vector<int>> res = Subsets(data);sort(res.begin(), res.end(), comp);vector<vector<int>> result;for (int i = 0; i < res.size(); i++){if (res[i].size() == k)result.push_back(res[i]);}return result;}int main(){const int n = 4;int a[n];for (int i = 0; i < n; i++)a[i] = i + 1;vector<int> data(begin(a), end(a));//===int k = 2;vector<vector<int>> res =Combination(data,k);for (int i = 0; i < res.size(); i++){for (int j = 0; j < res[i].size(); j++)cout << res[i][j] << " ";cout << endl;}}