SDUT 2498 AOE网上的关键路径

//SPFA
#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
#define N 10010
using namespace std;

struct Arcnode
{
int to;
int weight;
Arcnode *next;
};

Arcnode *List[N*5];

queue<int>Q;
int n, m;
int ans, flag;
int dis[N*5];
int path[N*5];
bool vis[N*5];
int Indegree
;
int Outdegree
;

void SPFA(int st)
{
int u;
memset(path, 0, sizeof(path));
memset(vis, 0, sizeof(vis));
memset(dis, 0, sizeof(dis));
vis[st] = 1;
Arcnode *tmp;
Q.push(st);
while(!Q.empty())
{
u = Q.front(), Q.pop(), vis[u] = 0;
tmp = List[u];
while(tmp)
{
int v = tmp -> to;
if(dis[v] < dis[u] + tmp -> weight)
{
dis[v] = dis[u] + tmp -> weight;
path[v] = u;
if(!vis[v])
{
vis[v] = 1;
Q.push(v);
}
}
if(dis[v] == dis[u] + tmp -> weight && u < path[v])
{
path[v] = u;
if(!vis[v])
{
vis[v] = 1;
Q.push(v);
}
}
tmp = tmp -> next;
}
}
cout << dis[ans] << endl;
int k = ans;
while(path[k] != 0)
{
cout << k << ' ' << path[k] << endl;
k = path[k];
}
}

int main()
{
while(cin >> n >> m)
{
memset(Indegree, 0, sizeof(Indegree));
memset(Outdegree, 0, sizeof(Outdegree));
memset(List, 0, sizeof(List));
while( m --)
{
int u, v, w;
cin >> u >> v >> w;
Indegree[u] ++;
Outdegree[v] ++;
Arcnode *tmp = new Arcnode;
tmp -> to = u;
tmp -> weight = w;
tmp -> next = NULL;
if(List[v] == NULL) List[v] = tmp;
else
{
tmp -> next = List[v];
List[v] = tmp;
}

}
for(int i = 1; i <= n; i++)
{
if(Indegree[i] == 0) flag = i;
if(Outdegree[i] == 0) ans = i;
}
SPFA(flag);
}
return 0;
}

//Bellman_Ford
#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
using namespace std;

struct edge
{
    int u, v, w;
} Edge[50010];

int n, m, k;
int ans;
int path[50010];
int dis[50010];
int Outdegree[50010];

void Bellman_Ford(int st);

int main()
{
    while(~scanf("%d %d", &n, &m))
    {
        memset(Edge, 0, sizeof(Edge));
        memset(Outdegree, 0, sizeof(Outdegree));
        for(int i = 1; i <= m; i++)
        {
            int u, v, w;
            scanf("%d %d %d", &u, &v, &w);
            Edge[i].u = v, Edge[i].v = u, Edge[i].w = w;
            Outdegree[v] ++;
        }

        for(int i = 1; i <= n; i++)
        {
            if(Outdegree[i] == 0)  {ans = i; break}
        }
        Bellman_Ford();
    }
    return 0;
}

void Bellman_Ford()
{
    memset(dis, 0, sizeof(dis));
    memset(path, 0, sizeof(path));
    for(int j = 2; j <= n; j++)//从dis(1)[u]递推出dis(2)[u]......dis(n)
.（忘了注释，差点把自己搞蒙了．．．悲哀，还是加上吧）
    {
    int tmp = 0;//排除冗余情况
    for(int i = 1; i <= m; i++)
     {

       if(dis[Edge[i].u] + Edge[i].w > dis[Edge[i].v] || (dis[Edge[i].u] + Edge[i].w == dis[Edge[i].v]
 &&Edge[i].u < path[Edge[i].v]))
        {
         dis[Edge[i].v] = dis[Edge[i].u] + Edge[i].w;
         path[Edge[i].v] = Edge[i].u;
         tmp = 1;
        }
     }
     if(tmp == 0) break;
    }
    printf("%d\n", dis[ans]);
    int k = ans;
    while(path[k] != 0)
    {
        printf("%d %d\n", k, path[k]);
        k = path[k];
    }
}