枚举排列组合(dfs)

可重复的排列

#include<iostream>  
using namespace std;
int n, m;
int dis[15]; //展示数组
int a[15];   //存放m个数
void dfs(int cnt) //cnt表示现在是第几个数
{
    if (cnt == m)
    {
        for (int i = 0; i < m; i++)
            cout << dis[i] << " ";
        cout << endl;
        return;
    }
    for (int i = 0; i < n; i++)
    {
        dis[cnt] = a[i];
        dfs(cnt + 1);
    }
}
int main()
{
    
    cin >> n >> m;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    dfs(0);
    return 0;
}

不可重复的排列

#include<iostream>  
#include<cstring>
using namespace std;
int n, m;
int dis[15];
int a[15];
int book[15];//标记数组 对应a里的每个数
void dfs(int cnt)
{
    if (cnt == m)
    {
        for (int i = 0; i < m; i++)
            cout << dis[i] << " ";
        cout << endl;
        return;
    }
    for (int i = 0; i < n; i++)
    {
        if (book[i] == 0)
        {
            dis[cnt] = a[i];
            book[i] = 1;
            dfs(cnt + 1);
            book[i] = 0;
        }
    }
}
int main()
{
    memset(book, 0, sizeof(book));
    cin >> n >> m;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    dfs(0);
    return 0;
}

枚举组合

#include<iostream>  
#include<cstring>
using namespace std;
int n, m;
int dis[15];
int a[15];
void dfs(int d,int cnt) //d表示标记位置
{
    if (cnt == m)
    {
        for (int i = 0; i < m; i++)
            cout << dis[i] << " ";
        cout << endl;
        return;
    }
    for (int i = d; i < n; i++)
    {
        dis[cnt] = a[i];
        dfs(i+1,cnt + 1);
    }
}
int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    dfs(0,0);
    return 0;
}