拓扑排序 -2025/11/22

拓扑排序

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10;

int e[N], ne[N], h[N], idx;
int n, m, d[N];
int q[N];

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

bool top_sort(){
	int hh = 0, tt = -1;
	for(int i = 1;i <= n; i++) {
		if(d[i] == 0) q[++ tt] = i;
	}
	
	while(hh <= tt){
		auto t = q[hh ++];
		for(int i = h[t]; i != -1; i = ne[i]){
			int j = e[i];
			d[j] --;
			if(d[j] == 0) q[++ tt] = j;
		}
	}
	
	return tt == n - 1;
}

int main(){
	// 单链表, h初始化为-1, 用于存储图时, 对于每一个头节点都要初始化为-1, 要不然会超时
	memset(h, -1 , sizeof h);
	
	cin >> n >> m;
	
	for(int i = 1; i <= m; i++){
		int a,b;
		cin >> a >> b;
		add(a , b);
		d[b] ++;
	}
	
	if(top_sort()){
		for(int i = 0;i < n; i++) cout << q[i] << " ";
	}
	else cout << "-1" << "\n";
	
	return 0;
}