hdoj2874 -- Connections between cities(LCA--tarjan离线)

Connections between cities

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 8041    Accepted Submission(s): 1994

Problem Description

After World War X, a lot of cities have been seriously damaged, and we need to rebuild those cities. However, some materials needed can only be produced in certain places. So we need to transport these materials from city to city. For most of roads had been totally destroyed during the war, there might be no path between two cities, no circle exists as well.
Now, your task comes. After giving you the condition of the roads, we want to know if there exists a path between any two cities. If the answer is yes, output the shortest path between them.

 

Input

Input consists of multiple problem instances.For each instance, first line contains three integers n, m and c, 2<=n<=10000, 0<=m<10000, 1<=c<=1000000. n represents the number of cities numbered from 1 to n. Following m lines, each line has three integers i, j and k, represent a road between city i and city j, with length k. Last c lines, two integers i, j each line, indicates a query of city i and city j.

 

Output

For each problem instance, one line for each query. If no path between two cities, output “Not connected”, otherwise output the length of the shortest path between them.

 

Sample Input

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

 

Sample Output

Not connected 6

Hint

Hint Huge input, scanf recommended.

 

Source

2009 Multi-University Training Contest 8 - Host by BJNU

 

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最短路;

#include <cstdio>
#include <cstring>

#define N 10010
#define M 20010
#define C 2000010

struct Edge{
    int to, next, dis;
    Edge() {}
    Edge(int to, int dis, int next): to(to), dis(dis), next(next){};
}E[M];

struct Edge2{
    int to, next, w;
    Edge2() {}
    Edge2(int to, int w, int next): to(to), w(w), next(next) {};
}E2[C];

int n, m, c, tot, tot2;
int head[N], head2[N], dis[N], f[N], vis[N];

void addEdge(int u, int v, int dis){ 
    E[tot]= Edge(v, dis, head[u]);
    head[u]=tot++;
    E[tot]= Edge(u, dis, head[v]);
    head[v]=tot++;
}

void addEdge2(int u, int v){
    E2[tot2]= Edge2(v, -1, head2[u]);
    head2[u]=tot2++;
    E2[tot2]= Edge2(u, -1, head2[v]);
    head2[v]=tot2++;
}
/*void addEdge(int u, int v, int dis) {
    E[tot].to = v; E[tot].next = head[u]; E[tot].dis = dis; head[u] = tot++;
    u = u ^ v; v = u ^ v; u = u ^ v;
    E[tot].to = v; E[tot].next = head[u]; E[tot].dis = dis; head[u] = tot++;
}

void addEdge2(int u, int v) {
    E2[tot2].to = v; E2[tot2].next = head2[u]; E2[tot2].w = -1; head2[u] = tot2++;
    u = u ^ v; v = u ^ v; u = u ^ v;
    E2[tot2].to = v; E2[tot2].next = head2[u]; E2[tot2].w = -1; head2[u] = tot2++;
}*/
void init()
{
    memset(head, -1, sizeof(head));
    memset(head2, -1, sizeof(head2));
    tot=tot2=0;
    
    int u, v, d;
    for(int i=0; i< m; i++)
    {
        scanf("%d%d%d", &u, &v, &d);
        addEdge(u, v, d); 
    } 
    
    for(int i=0; i<c; i++)
    {
        scanf("%d%d", &u, &v);
        addEdge2(u, v);
    }
    memset(vis, 0, sizeof(vis));
}

int find(int x){
    return x==f[x]?  x: f[x]=find(f[x]);
}

void tarjan(int u, int time)
{
    vis[u]= time;
    f[u]= u;
    
    int v;
    for(int i=head[u]; ~i; i=E[i].next)
    {
        v=E[i].to;
        if(vis[v])
            continue;
        dis[v]= dis[u]+ E[i].dis;
        tarjan(v, time);
        f[v]= u;    
    } 
    
    for(int i= head2[u]; ~i; i=E2[i].next)
    {
        v=E2[i].to;
        if(vis[v]== time)
            E2[i].w= E2[i^1].w = dis[u]+dis[v]- 2*dis[find(v)];
    }
} 
void solve()
{
    int cnt=1;
    for(int i=1; i<=n; i++){
        if(!vis[i]){
            dis[i]= 0;
            tarjan(i, cnt); 
        } 
        cnt++;
    }
    
    for(int i=0; i< tot2; i +=2){
        if(E2[i].w == -1)
            printf("Not connected
");
        else
            printf("%d
", E2[i].w)  ;
    }
}
int main()
{
    while(scanf("%d%d%d", &n, &m, &c) != EOF)
    {
        init();
        solve();
    }
    return 0;
}