why！why！

#include<iostream>
#include<cstdio>
using namespace std;
int n,m;
int a[30],b[255];
void dfs(int step){
    if(step==m+1){
        for(int i=1;i<=m;i++){
            cout<<a[i]<<' ';
        }
        cout<<endl;
        return ;
    }
    else{
        for(int i=1;i<=n;i++){
            if(b[i]==0 && i>=a[step-1]){
                a[step]=i;
                b[i]=1;
                dfs(step+1);
                b[i]=0;
            }
        }
    }
}
int main(){
    freopen("A.in","r",stdin);
    freopen("A.out","w",stdout);
    cin>>n>>m;
    dfs(1);
    return 0;
}

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