关键活动

#include<stdio.h>
#include<stdlib.h>

#define MAXN 102 
#define INFINITY 999

int G[MAXN][MAXN] ;//图
int earliest[MAXN];//最早开始时间
int latest[MAXN];//最晚开始时间
int indegree[MAXN];//入度
int outdegree[MAXN];//出度
int max(int a, int b)
{
    if(a > b)
    {
        return a;
    }
    else
    {
        return b;
    }
}
int min(int a, int b)
{
    if(a < b)
    {
        return a;
    }
    else
    {
        return b;
    }
}

void late_time(int n,int max)
{
    int queue[n];//建立一个简单队列
    int first = -1,rear = -1;

    for(int i=1; i<=n; i++)//将入度为0的节点压进去 
    {
        if(outdegree[i] == 0)
        {
            rear++;
            queue[rear] = i; //入队
            
            latest[i] = max;
        }
    } 


    while(first < rear)
    {
        first++;
        int v = queue[first];//出队
        
        for( int i=n; i>=1; i--) //对V的每个邻接点处理
        {
            if(G[i][v]>=0)
            {
                outdegree[i]--;//出度减一
                latest[i] = min(latest[i],latest[v]-G[i][v]); 
                if(outdegree[i] == 0)
                {
                    queue[++rear] = i; 
                }           
            }

        } 
    }
}

int early_time(int n)
{
    int queue[n];//建立一个简单队列
    int first = -1,rear = -1;

    for(int i=1; i<=n; i++)//将入度为0的节点压进去 
    {
        if(indegree[i] == 0)
        {   
            queue[++rear] = i; //入队
        }
    } 

    int cnt = 0;
    while(first < rear)
    {
        int v = queue[++first];//出队
        cnt++;
        for( int i=1; i<=n; i++) //对V的每个邻接点处理
        {
            if(G[v][i]>=0)
            {
                indegree[i]--;//入度减一
                earliest[i] = max(earliest[i],earliest[v]+G[v][i]);
                if(indegree[i] == 0) 
                {
                queue[++rear] = i; 
                }           
            }

        } 
    }

    int ans = 0;
    if (cnt != n)//不能拓扑排序 
    {
        ans = -1;
    }
    else
    {
        ans = earliest[0];//可以拓扑排序，找最大值 
        for(int i=1; i<=n; i++)
        {
            if(earliest[i] > ans)
            {
                ans = earliest[i];
            } 
        }
    }

    return ans;
}

void intial(int n)
{
    int i,j;
    for( i=1;i<=n;i++)//节点从1开始 
    {
        for(j=0;j<=n;j++)
        {
            G[i][j] = -1;
        }
        earliest[i] = 0;
        indegree[i] = 0;
        outdegree[i] = 0;
        latest[i] = INFINITY; 
    }

}


int main()
{
    int n,m;
    scanf("%d %d",&n,&m);//读入节点，读入活动数
    intial(n);

    int i;
    int s,e,c;//source,end,cost
    for(i=1;i<=m;i++)//读入数据 
    {
        scanf("%d %d %d",&s,&e,&c);
        G[s][e] = c;//有向边 
        indegree[e]++;//入度初始化 
        outdegree[s]++;//出度初始化 
    }

    int flag;
    flag = early_time(n);
    if(flag == -1)
    {
        printf("0\n");
    }
    else
    {
        printf("%d\n",flag);
        late_time(n,flag);
        for (int i = 1; i <= n; i++)
        {  
            if (earliest[i] != latest[i])  
                continue;  
            for (int j = n; j >= 1; j--)
            {  
                if (G[i][j] >= 0 && earliest[j] == latest[j] 
                && (latest[j] - earliest[i] == G[i][j]))  
                    printf("%d->%d\n", i, j);  
            }  
        }  
    }

    return 0; 
}