Examples of topological sequences

subject ：

Given a n A little bit m Directed graph of strip edge , There may be double edges and self rings in the graph .

Please output any topological sequence of the directed graph , If the topological sequence does not exist , The output -1.

If a sequence consisting of all the points in the graph A Satisfy ： For each edge in the graph (x, y),x stay A All appear in y Before , said A Is a topological sequence of the graph .

Input format

The first line contains two integers n and m

Next m That's ok , Each line contains two integers x and y, Indication point x Sum point y There is a directed edge between (x, y).

Output format

All in one line , If there is a topological sequence , Then the topology sequence is output .

Otherwise output -1.

Data range

1≤n,m≤10^5
sample input ：

3 3
1 2
2 3
1 3

sample output ：

1 2 3

Code ：

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;
const int N=1e5+10;
int h[N],e[N],ne[N],idx,q[N],d[N],n,m,b[N];

void add(int a,int b){
	e[idx]=b,ne[idx]=h[a],h[a]=idx++;
}

bool topsort(){
	int hh=0,tt=-1;// Define the head and tail of the team  
	for(int i=1;i<=n;i++){
		if(!d[i]) q[++tt]=i;// Take out all the data with zero queue and save it in q 
	}
	while(hh<=tt){
		int v=q[hh++];
		for(int i=h[v];i!=-1;i=ne[i]){
			int w=e[i];
			d[w]--;// Take out a number , Join the team minus one  
			if(!d[w]) q[++tt]=w;// If the enrollment is zero, deposit q 
		}
	}
	if(tt==n-1){
		for(int i=0;i<n;i++) cout<<q[i]<<" ";
		cout<<endl;
	}
}

int main(){
	cin>>n>>m;
	memset(h,-1,sizeof h);
	for(int i=0;i<m;i++){
		int a,b; 
		cin>>a>>b;
		add(a,b);
		d[b]++;
	}
	topsort();
	return 0;
}