C++ :

#include <bits/stdc++.h>
using namespace std;
int a[100010] = {0};
int n;
int r; 
bool b[100010];//标记该数是否用过

void show(){
	int i;
	for(i = 1;i <= r;i++){
		cout<<a[i]<<" ";
	}
	cout<<endl;
} 

//回溯找数 
int search(int k){
	int i;
	for(i = 1;i <= n;i++){
		//如果i没用过 
		if(b[i] == false){
			a[k] = i;//结果存入数组 
			b[i] = true;//标记为用过
			//够数量，输出结果 
			if(k == r){
				show();
			} else{
				//继续找数
				search(k + 1); 
			}
			//回溯
			b[i] = false;//标记该数没用过 
		}
	}
} 

int main(){
	cin>>n>>r;
	search(1);
}

Python :

import math
import sys
n,r=list(map(int,input().split()))

vis=[0]*(n+1)
a=[0]*(n+1)

def df(step):
    if step>r:
        for item in a[1:1+r]:
            print(item,end=" ")
        print()
        return 
    for i in range(1,n+1):
        if vis[i]==0:
            a[step]=i
            vis[i]=1
            df(step+1)
            vis[i]=0
df(1)