08-图8 How Long Does It Take（25 分）

08-图8 How Long Does It Take（25 分）

Given the relations of all the activities of a project, you are supposed to find the earliest completion time of the project.

Input Specification:

Each input file contains one test case. Each case starts with a line containing two positive integers N (≤100),
the number of activity check points (hence it is assumed that the check points are numbered from 0 to N−1),
and M,
the number of activities. Then M lines
follow, each gives the description of an activity. For the 

i

-th
activity, three non-negative numbers are given: 

S[i]

, 

E[i]

,
and 

L[i]

, where 

S[i]

 is
the index of the starting check point, 

E[i]

 of
the ending check point, and 

L[i]

 the lasting
time of the activity. The numbers in a line are separated by a space.

Output Specification:

For each test case, if the scheduling is possible, print in a line its earliest completion time; or simply output "Impossible".

Sample Input 1:

9 12
0 1 6
0 2 4
0 3 5
1 4 1
2 4 1
3 5 2
5 4 0
4 6 9
4 7 7
5 7 4
6 8 2
7 8 4

Sample Output 1:

18

Sample Input 2:

4 5
0 1 1
0 2 2
2 1 3
1 3 4
3 2 5

#include<iostream>
#include<fstream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#include<queue>
#include<functional>

using namespace std;
//ifstream inFile("C:\\Users\\DELL\\Desktop\\in.txt", ios::in);
const int MaxVertexNum = 100;
typedef int Vertex;
typedef int WeightType;
typedef char DatatType;

//边的定义
typedef struct ENode *PtrToENode;
struct ENode {
Vertex V1, V2;
WeightType Weight;
};
typedef PtrToENode Edge;

//邻接点的定义
typedef struct AdjVNode *PtrToAdjVNode;
struct AdjVNode {
WeightType Weight;
int earlisttime;//最早完成时间
int lasttime;//最后完成时间
Vertex AdjV;
PtrToAdjVNode Next;
};

//顶点表头结点的定义
typedef struct VNode {
int earlisttime;//最早完成时间
PtrToAdjVNode FirstEdge;
DatatType Data;
}AdjList[MaxVertexNum];

//图结点的定义
typedef struct GNode* PtrToGNode;
struct GNode {
int Nv;
int Ne;
AdjList G;
};
typedef  PtrToGNode LGraph;

LGraph CreateGraph(int VertexNum)
{
LGraph Graph = new GNode;
Graph->Nv = VertexNum;
Graph->Ne = 0;
for (int i = 0; i < Graph->Nv; ++i) {
Graph->G[i].FirstEdge = nullptr;
Graph->G[i].earlisttime = 0;
}
return Graph;
}

//插入有向边<V1,V2>
void InsertEdge(LGraph Graph, Edge E)
{
PtrToAdjVNode p = new AdjVNode;
p->AdjV = E->V2;
p->Weight = E->Weight;
p->earlisttime = 0;
p->Next = Graph->G[E->V1].FirstEdge;
Graph->G[E->V1].FirstEdge = p;
}
LGraph BulidGraph()
{
int Nv;
cin >> Nv;
LGraph Graph = CreateGraph(Nv);
cin >> Graph->Ne;
if (Graph->Ne) {
Edge E = new ENode;
for (int i = 0; i < Graph->Ne; ++i) {
cin >> E->V1 >> E->V2 >> E->Weight;
InsertEdge(Graph, E);
}
}
return Graph;
}
void Print(LGraph Graph)
{
if (Graph->Nv) {
for (int i = 0; i < Graph->Nv; ++i) {
PtrToAdjVNode p = Graph->G[i].FirstEdge;
while (p) {
cout << p->AdjV << " ";
p = p->Next;
}
cout << endl;
}
}
}

bool TopSort(LGraph Graph, Vertex TopOrder[],int& ret,int m[])
{

ret = 0;
//对Graph进行拓扑排序，TopOrder[]顺序存储排序后的顶点下标
int Indegree[MaxVertexNum], cnt;
queue<int> Q;
//初始化Indegree[]
for (int V = 0; V < Graph->Nv; ++V) {
Indegree[V] = 0;
}
//遍历图得到Indegree[]
for (int V = 0; V < Graph->Nv; ++V) {
for (PtrToAdjVNode W = Graph->G[V].FirstEdge; W; W=W->Next ) {
Indegree[W->AdjV]++;//对有向边<V，W->AdjV>累计终点的入度
}
}
//将所有入度为0的点入队
for (int V = 0; V < Graph->Nv; ++V) {
if (Indegree[V] == 0) {
Q.push(V);
}
}
//下面进行拓扑排序
cnt = 0;
while (Q.size()) {
int V = Q.front();//弹出一个入度为0的点
Q.pop();
TopOrder[cnt++] = V;//将之存为结果序列的下一个元素
//对V的每个邻接点W->AdjV
for (PtrToAdjVNode W = Graph->G[V].FirstEdge; W; W = W->Next) {
if (--Indegree[W->AdjV] == 0) {//若删除V使得W->AdjV入度为零
Q.push(W->AdjV );
}
if (Graph->G[V].earlisttime + W->Weight >W->earlisttime) {
W->earlisttime = Graph->G[V].earlisttime  + W->Weight;
Graph->G[W->AdjV ].earlisttime = W->earlisttime;
m[W->AdjV] = ret;
if (ret < W->earlisttime) {
ret = W->earlisttime;
}
}
}
}
if (cnt != Graph->Nv) {
return false;//说明图中有回路，返回不成功的标志
}
else {
return true;
}
}
int main()
{
LGraph Graph = BulidGraph();
//Print(Graph);
Vertex TopOrder[MaxVertexNum] ;
Vertex m[MaxVertexNum];
int ret = 0;
if (TopSort(Graph, TopOrder,ret,m)) {
cout << ret << endl;
}
else {
cout << "Impossible" << endl;
}

//delete Graph;
//	inFile.close();
system("pause");
return 0;
}