hdu 2874 Connections between cities

LCA

题意：询问LCA，不过图不连通，如果两点不连通输出那串英文否则输出两点间的距离，模板题

#include <iostream>

#include <cstdio>

#include <cstring>

using namespace std;

#define N 10010

#define M 10010

#define Q 1000010



int head[N];

struct edge{

    int u,v,w,next;

}e[2*M];

int __head[N];

struct ask{

    int u,v,lca,next;

}ea[2*Q];

int dir[N],fa[N],vis[N];



inline void add_edge(int u ,int v ,int w ,int &k)

{

    e[k].u = u; e[k].v = v; e[k].w = w;

    e[k].next = head[u]; head[u] = k++;

}

inline void add_ask(int u ,int v ,int &k)

{

    ea[k].u = u; ea[k].v = v; ea[k].lca = -1;

    ea[k].next = __head[u]; __head[u] = k++;

}



int find(int x){

    return  x == fa[x] ? x : fa[x] = find(fa[x]);

}



void Tarjan(int u ,int c)

{

    vis[u] = c; fa[u] = u;

    for(int k=head[u]; k!=-1; k=e[k].next)

        if(!vis[e[k].v])

        {

            int v = e[k].v , w = e[k].w;

            dir[v] = dir[u] + w;

            Tarjan(v,c);

            fa[v] = u;

        }

    for(int k=__head[u]; k!=-1; k=ea[k].next)

        if(vis[ea[k].v] == c)

            ea[k].lca = ea[k^1].lca = find(ea[k].v);

}



int main()

{

    int n,m,q,k;

    while(scanf("%d%d%d",&n,&m,&q)!=EOF)

    {

        memset(head,-1,sizeof(head));

        memset(__head,-1,sizeof(__head));

        memset(vis,0,sizeof(vis));

        k = 0;

        for(int i=0; i<m; i++)

        {

            int u,v,w;

            scanf("%d%d%d",&u,&v,&w);

            add_edge(u,v,w,k);

            add_edge(v,u,w,k);

        }

        k = 0;

        for(int i=0; i<q; i++)

        {

            int u,v;

            scanf("%d%d",&u,&v);

            add_ask(u,v,k);

            add_ask(v,u,k);

        }

        k = 0;

        for(int i=1; i<=n; i++)

            if(!vis[i])

            {

                dir[i] = 0;

                Tarjan(i,++k);

            }

        for(int i=0; i<q; i++)

        {

            int s = i*2 , u = ea[s].u , v = ea[s].v , lca = ea[s].lca;

            if(lca == -1) printf("Not connected\n");

            else          printf("%d\n",dir[u] + dir[v] - 2*dir[lca]);

        }

    }

    return 0;

}