性质

一种邻接表的写法

关键点：

• 数据结构

  // 边
  class Edge {int next; // 指向相同起始点的下一条边int to; // 邻接点int w; // 权重
  }
  Edge[] edge = new Edge[9];
  // edge[cnt]表示编号为cnt的边// 用数组表示
  int[] next = new int[MAX];
  int[] to = new int[MAX];
  int[] w = new int[MAX];
  // 即next[j]表示与编号为j的边的起始点相同的下一条边
  //   to[j]表示编号为j的边的邻接点
  //   w[j]表示编号为j的边的权重//存放每个起始点的边头指针
  int[] head = new int[MAX]; 
  // 即head[i]表示以i为起点的第一条边的序号
  

• 加边操作

  addEdge(int from , int to, int w){// cnt为边的序号edge[cnt].to = to;edge[cnt].w = w;// 头插法edge[cnt].next = head[from];head[from] = cnt
  }
  

• 遍历某一起始点的所有边

  int t = head[i]; // 假设不存在为-1
  while(t != -1){....t = edge[t].next
  }
  

附：用链式前向星求拓扑序列

import java.util.*;
import java.io.*;// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {public static int MAXN = 200002;public static int MAXM = 200002;public static int[] head = new int[MAXN];public static int[] indegree = new int[MAXN];// 入度表public static int[] q = new int[MAXN];public static int h = 0; // 队列头public static int r = 0; // 队列尾// edgepublic static int[] next = new int[MAXM];public static int[] to = new int[MAXM];public static int cnt = 0; // 边的编号public static void main(String[] args) throws Exception {BufferedReader br = new BufferedReader(new InputStreamReader(System.in));StringBuilder re = new StringBuilder();String str;// 满足即存在环String[] s = br.readLine().split(" ");int n = Integer.parseInt(s[0]);int m = Integer.parseInt(s[1]);int count = 0 ; // 记录出队的节点数Arrays.fill(head, 0, n + 1, -1);if (m > n * (n - 1) / 2 ) {System.out.println("-1");return;}// 存图while ((str = br.readLine()) != null) {String[] temp = str.split(" ");int from = Integer.parseInt(temp[0]);int to = Integer.parseInt(temp[1]);addEdge(from, to);indegree[to]++;}// 初始化入度表for (int i = 1 ; i < n + 1; i++) {if(indegree[i] == 0){q[r++] = i; }}while(h < r){int no = q[h++];count++;re.append(no + " ");updateIndegree(no);}if(count == n){System.out.println(re);}else{System.out.println("-1");}br.close();}public static void addEdge(int from, int t) {to[cnt] = t;next[cnt] = head[from];head[from] = cnt++;  }public static void updateIndegree(int node){int i = head[node];while(i != -1){indegree[to[i]]--;if( indegree[to[i]] == 0){q[r++] = (to[i]);}i = next[i];}}
}