递归实现组合型枚举

#include<iostream>
#include<vector>int n, m;
std::vector<int>res;
bool st[30];void Print()
{for(int i=0;i<res.size();i++){printf("%d ",res[i]);}puts("");
}void dfs(int num)
{if (res.size() == m){Print();return;}for (int i = num; i <= n; i++){if (!st[i]){st[i] = true;res.push_back(i);if (res.size() == 1 && res[0] > (n-m+1)){res.pop_back();st[i] = false;continue;}dfs(i + 1);st[i] = false;res.pop_back();}}
}int main(void)
{scanf("%d %d", &n, &m);dfs(1);return 0;
}

解法二

#include<iostream>
#include<vector>int n, m;
std::vector<int>res;
bool st[30];void dfs(int start)
{if(res.size()==m){for(int i=0;i<res.size();i++){printf("%d ",res[i]);}puts("");return;}for(int i=start;i<=n;i++){res.push_back(i);dfs(i+1);res.pop_back();}
}int main(void)
{scanf("%d %d", &n, &m);dfs(1);return 0;
}