93. Recursive implementation of combinatorial enumeration

#include<iostream>
using namespace std;

int n,m;
//u Indicates the current number of digits that need to be enumerated ,k Indicates current needs   Enumerate the number 
void dfs(int u,int k,int state){
    if(k == m){
        for(int i = 0;i < n;i++)
            if(state >> i & 1) cout << i + 1 << ' ';
        cout << endl;
        return;
    }
    if(u == n)  return; //   Enumeration to the last number still does not conform to enumeration m The condition of number , Is illegal 
    
    dfs(u + 1,k + 1,state | 1 << u);
    dfs(u + 1,k,state); // Be careful , This statement should be below the previous one , You should enumerate and select this number first , Enumerate again and don't choose , Otherwise, the output order is wrong 
}

int main()
{
    cin >> n >> m;
    dfs(0,0,0);
    return 0;
}