DFS即可

#include <bits/stdc++.h>
using namespace std;
const int N = 20;
int a[N];
int b[N];
int n,m;
void dfs(int x,int start){
    if (x > m) {
        for (int i = 1; i <= m; ++i) {
            printf("%d ",b[i]);
        }
        printf("\n");
        return;
    }
    for (int i = start; i <= n; ++i) {
        b[x] = a[i];
        dfs(x + 1,i + 1);
    }
}
int main(){
    scanf("%d %d",&n,&m);
    for (int i = 1; i <= n; ++i) {
        scanf("%d",&a[i]);
    }
    sort(a + 1, a + n + 1);
    dfs(1,1);
    return 0;
}