Connections between cities（bfs的倍增+数组）

看题解的时候看到一个优秀的思想：用一个数组标记每个点所属数号，如果两个点不是同一个数号， 就证明两点不能达。

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
const int maxn = 1e4+20;
using namespace std;

int n,m,c,cnt,head[maxn],deep[maxn],dis[maxn],vis[maxn],cas,fa[maxn][30];
struct node{
    int to;
    int next;
    int w;
}e[maxn<<1];

void init(){
    cnt = 0;
    cas = 0;
    memset(vis,0,sizeof(vis));
    memset(deep,0,sizeof(deep));
    memset(dis,0,sizeof(dis));
    memset(head,-1,sizeof(head));
}

void addedge(int u,int v,int w){
    e[cnt].to = v;
    e[cnt].next = head[u];
    e[cnt].w = w;
    head[u] = cnt++;
}

void bfs(int root){
    queue<int>q;
    dis[root] = 0; deep[root] = 0; fa[root][0] = 0;
    vis[root] = cas;
    q.push(root);
    while(!q.empty()){
        int u = q.front(); q.pop();
        for(int i = 1 ; i < 20 ; i++)   fa[u][i] = fa[fa[u][i-1]][i-1];
        for(int i = head[u] ; ~i ; i = e[i].next){
            int v = e[i].to;
            if(fa[u][0] == v)   continue;
            deep[v] = deep[u] + 1;
            dis[v] = dis[u] + e[i].w;
            vis[v] = cas;
            fa[v][0] = u;
            q.push(v);
        }
    }
}

int LCA(int x,int y){
    if(deep[x] < deep[y])   swap(x,y);
    for(int i = 19 ; i >= 0 ; i--)
        if(deep[x] - (1<<i) >= deep[y])
            x = fa[x][i];
    if(x == y)  return x;
    for(int i = 19 ; i >= 0 ; i--){
        if(fa[x][i] != fa[y][i]){
            x = fa[x][i];
            y = fa[y][i];
        }
    }
//    for(int i = 19 ; i >=0 ; i--)
//    if(fa[x][i] != fa[y][i]){
//
//    }
    return fa[x][0];
}

int main(){
    while(~scanf("%d%d%d",&n,&m,&c)){
        int u,v,w;
        init();
        for(int i = 0; i < m ; i++){
            scanf("%d%d%d",&u,&v,&w);
            addedge(u,v,w);
            addedge(v,u,w);
        }
        for(int i = 1; i <= n ; i++){
            if(!vis[i]){
                cas++;
                bfs(i);
            }
        }
//        for(int i = 1; i <= n ; i++){
//            printf("%d ",vis[i]);
//        }
//        printf("\n\n");
        for(int i = 1 ; i <= c ;i++){
            scanf("%d%d",&u,&v);
            if(vis[u] != vis[v])    printf("Not connected\n");
            else printf("%d\n",dis[u]+dis[v]-2*dis[LCA(u,v)]);
        }
    }
    return 0;
}


/*
5 1 5
1 5 2
1 5
4 5
1 3
2 4
1 4
*/