有向图的拓扑排序 链式前向星

AcWing 848. 有向图的拓扑序列

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

const int N = 100005;

struct Node {
   
    int nxt, to;
}nodes[N];

int vers[N], cnt;
int q[N], d[N]; //q为队列数组，d记录每个节点的入度；
int len;
int n, m;

void add(int u, int v) 
{
   
    nodes[++cnt].to = v;
    nodes[cnt].nxt = vers[u];
    vers[u] = cnt;
}

bool topsort() 
{
      
    int head = 0;
    for (int i = 1; i <= n; ++i) {
   
        if (d[i] == 0) {
   
            q[len++] = i;   //将入度为0的点加入队列
        }
    }

    while (head != len) {
   
        for (int p = vers[q[head]]; p != 0; p = nodes[p].nxt) {
   
            int j = nodes[p].to;
            --d[j]; //将这条边删除，入度减一
            //如果入度已经为0，就加入队列中
            if (d[j] == 0) {
   
                q[len++] =j;
            }
        }
        ++head;
    }

    //因为如果无环的话，每个节点最多入队一次，队列最终入队的元素数量就等于节点数量
    return len == n;
}

int main() 
{
   
#ifndef ONLINE_JUDGE
    freopen("D:/VS CODE/C++/in.txt", "r", stdin);
    freopen("D:/VS CODE/C++/out.txt", "w", stdout);
#endif
    cin >> n >> m;

    for (int i = 0; i < m; ++i) {
   
        int u, v;
        scanf("%d %d", &u, &v);
        add(u, v);
        ++d[v]; //增加入度
    }

    bool first = true;
    if (topsort()) {
   
        for (int i = 0; i < len; ++i) {
   
            printf(first ? "%d" : " %d", q[i]);
            first = false;
        }
    }
    else {
   
        printf("-1");
    }

    fclose(stdin);
    fclose(stdout);
    return 0;
}