HDU2647（逆向拓扑排序）

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=2647

package D0731;

/*
 * 题目大意：
 * 发奖金，如果能够实现每个人的需求就发，需求要满足拓扑排序。
 * 这个题目使用逆向的拓扑图更方便
 * 如果需求满足拓扑排序结果为n*888+(n/2*(n-1))
 * */
import java.util.*;
import java.io.*;

public class HDU2647 {

	static int n, m;
	static int[] indegree;// 顶点的入度
	static int index;// 拓扑排序的长度
	static List<ArrayList<Integer>> G = new ArrayList<ArrayList<Integer>>();// 邻接表
	static Queue<Integer> que;

	// /拓扑排序
	private static int topSort() {
		int[] rewards = new int[n + 1];// 工资-888
		int ans = 0;
		index = 0;
		que = new LinkedList<Integer>();

		for (int i = 1; i <= n; i++)
			if (indegree[i] == 0)
				que.add(i);

		while (!que.isEmpty()) {
			int v = que.poll();
			index++;
			for (int i : G.get(v)) {
				indegree[i]--;
				if (indegree[i] == 0) {
					que.add(i);
					rewards[i] = rewards[v] + 1;
					ans += rewards[i];
				}
			}
		}
		return ans;
	}

	public static void main(String[] args) throws IOException {
		StreamTokenizer st = new StreamTokenizer(new BufferedReader(
				new InputStreamReader(System.in)));
		PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

		while (st.nextToken() != StreamTokenizer.TT_EOF) {
			n = (int) st.nval;
			st.nextToken();
			m = (int) st.nval;
			indegree = new int[n + 1];
			G.clear();
			for (int i = 0; i <= n; i++)
				G.add(new ArrayList<Integer>());
			while (m-- > 0) {
				st.nextToken();
				int u = (int) st.nval;
				st.nextToken();
				int v = (int) st.nval;
				// 建立逆向的方向拓扑图，
				if (!G.get(v).contains(u)) {// 注意重边
					G.get(v).add(u);
					indegree[u]++;
				}
			}

			int ans = topSort();
			if(index==n)out.println(ans+n*888);
			else out.println(-1);
		}
		out.flush();

	}

}