hdu2647 Reward--拓扑排序

原题链接： http://acm.hdu.edu.cn/showproblem.php?pid=2647

一：原题内容

Problem Description

Dandelion's uncle is a boss of a factory. As the spring festival is coming , he wants to distribute rewards to his workers. Now he has a trouble about how to distribute the rewards.
The workers will compare their rewards ,and some one may have demands of the distributing of rewards ,just like a's reward should more than b's.Dandelion's unclue wants to fulfill all the demands, of course ,he wants to use the least money.Every work's reward will be at least 888 , because it's a lucky number.

Input

One line with two integers n and m ,stands for the number of works and the number of demands .(n<=10000,m<=20000)
then m lines ,each line contains two integers a and b ,stands for a's reward should be more than b's.

Output

For every case ,print the least money dandelion 's uncle needs to distribute .If it's impossible to fulfill all the works' demands ,print -1.

 

Sample Input

  

   2 1
1 2
2 2
1 2
2 1
  

Sample Output

  

   1777
-1
  

二：分析理解

使用一个reward数组保存第i个人能拿到的奖励，最后的结果只要把这n个加起来就可以

三：AC代码

#include<iostream>    
#include<string.h>  
#include<algorithm>  

using namespace std;

#define N 10005

struct Node
{
	int v;
	int next;
};

Node node[2 * N];
int inDegree[N];
int reward[N];
int head[N];
int sta[N];
int num;
int n, m;

void Join(int u, int v)
{
	node[num].v = v;
	node[num].next = head[u];
	head[u] = num++;
}

bool TopoSort()
{
	int sum = 0;
	int top = 0;
	for (int i = 1; i <= n; i++)
	{
		if (inDegree[i] == 0)
		{
			inDegree[i]--;
			sta[++top] = i;
			reward[i] = 888;
		}
	}
	while (top)
	{
		int u = sta[top--];
		sum++;
		for (int i = head[u]; i != -1; i = node[i].next)
		{
			int v = node[i].v;
			inDegree[v]--;
			reward[v] = max(reward[v], reward[u] + 1);
			if (inDegree[v] == 0)
			{
				sta[++top] = v;
				inDegree[v]--;
			}
		}
	}

	if (sum == n)
		return true;
	else
		return false;
}

int main()
{
	while (~scanf("%d%d", &n, &m))
	{
		num = 0;
		memset(inDegree, 0, sizeof(inDegree));
		memset(reward, 0, sizeof(reward));
		memset(head, -1, sizeof(head));

		int u, v;
		while (m--)
		{
			scanf("%d%d", &v, &u);
			Join(u, v);
			inDegree[v]++;
		}
		
		if (TopoSort())
		{
			for (int i = 2; i <= n; i++)
				reward[i] += reward[i - 1];
			printf("%d\n", reward[n]);
		}
		else
			printf("-1\n");
	}

	return 0;
}