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;
}
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