TLE一个点，求助

#include<iostream>

using namespace std;
int n,sum,a[10010],b[10010],f,y[21][21];
void yang(int n){
    y[1][1]=1;
    for(int i=1;i<=n;i++){
        y[i][1]=1;
        y[i][i]=1;
        for(int j=2;j<i;j++){
            y[i][j]=y[i-1][j]+y[i-1][j-1];
        }
    }
}
void dfs(int s,int x){
    if(f)return;
	if(s==n&&f==0){int ans=0;
        for(int i=1;i<=n;i++){
	    ans+=y[n][i]*b[i];
        }if(ans==sum){
        	for(int i=1;i<=n;i++)cout<<b[i]<<" ";
        	f=1;
		}
		return;
	}
	for(int i=1;i<=n;i++){
		int xx=x+i;
		if(a[i]==0&&xx<=sum){
			b[s+1]=i,a[i]=1;
		dfs(s+1,xx);
		    a[i]=0;
		}
	}
}
signed main(){
cin>>n>>sum;
    yang(n);
	dfs(0,0);
	return 0;
}