5-11 关键活动 (30分)

#include <iostream>
#include <vector>
#include <queue>

using namespace std;

struct node
{
	int next, time;
};

int degree[2][110], t[2][110], maxtime;
vector<node> v[2][110];

int torder(int index, int n)
{
	int i;
	queue<int> q;

	for(i = 1; i <= n; i++)
	{
		if(degree[index][i] == 0)
		{
			if(index == 1)
			{
				t[1][i] = maxtime;
			}

			q.push(i);
		}
	}

	int cur, size, next, nexttime[2], curtime, count = 0;
	while(q.size() > 0)
	{
		cur = q.front();
		q.pop();

		count++;

		size = v[index][cur].size();
		for(i = 0; i < size; i++)
		{
			next = v[index][cur][i].next;
			degree[index][next]--;

			if(degree[index][next] == 0)
			{
				q.push(next);
			}

			curtime = t[index][cur];
			nexttime[0] = curtime + v[index][cur][i].time;
			nexttime[1] = curtime - v[index][cur][i].time;

			if(index == 0 && nexttime[0] > t[0][next])
			{
				t[0][next] = nexttime[0];
			}
			else if(index == 1 && nexttime[1] < t[1][next])
			{
				t[1][next] = nexttime[1];
			}
		}

		if(index == 0 && t[0][cur] > maxtime)
		{
			maxtime = t[0][cur];
		}
	}

	if(count < n)
	{
		return 0;
	}

	return 1;
}

int main()
{
	int n, m;
	scanf("%d%d", &n, &m);

	int i, a, b;
	node nod;

	for(i = 1; i <= m; i++)
	{
		scanf("%d%d%d", &a, &b, &nod.time);

		nod.next = b;
		v[0][a].push_back(nod);

		nod.next = a;
		v[1][b].push_back(nod);

		degree[1][a]++;
		degree[0][b]++;
	}

	for(i = 1; i <= n; i++)
	{
		t[0][i] = 0;
		t[1][i] = 100000000;
	}

	for(i = 0; i <= 1; i++)
	{
		if(torder(i, n) == 0)
		{
			printf("0\n");
			return 0;
		}
	}

	printf("%d\n", maxtime);

	int size, j, next;
	for(i = 1; i <= n; i++)
	{
		size = v[0][i].size();
		for(j = size - 1; j >= 0; j--)
		{
			next = v[0][i][j].next;
			if(t[1][next] - t[0][i] == v[0][i][j].time)
			{
				printf("%d->%d\n", i, next);
			}
		}
	}

	system("pause");
	return 0;
}