hdu2874 Connections between cities(LCA)

自己写的T了，不知道为什么……以后知道了再说把，这个是T的代码

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;struct node{int to,nex,wei;}edge[20005];int head[10005*2],cnt,dis[10005],dep[10005],f[10005][20];int fa[10005*2];void add(int u,int v,int w){edge[cnt].to=v;edge[cnt].nex=head[u];edge[cnt].wei=w;head[u]=cnt++;}int find(int x){      while(fa[x]!=x){          x=fa[x];      }      return x;  }  void dfs(int root,int d,int val,int fa){//根，深度，权值，父亲dis[root]=val;        f[d][0]=fa;dep[root]=d;for(int i=head[root];~i;i=edge[i].nex){int v=edge[i].to;if(v==fa)continue;dfs(v,d+1,val+edge[i].wei,root);}}int lca(int x,int y){    if(dep[x]<dep[y])swap(x,y);//令x为深度较深的点    for(int i=16;i>=0;i--)if(dep[f[x][i]]>=dep[y])x=f[x][i];//让x向上走到与y同一深度    if(x==y)return x; //如果直接是lca，直接返回    for(int i=16;i>=0;i--)if(f[x][i]!=f[y][i])x=f[x][i],y=f[y][i];//x，y同时向上走，直到父节点相同    return f[x][0]; //返回父节点}int main(){int n,m,c;while(~scanf("%d%d%d",&n,&m,&c)){int i,j;memset(head,-1,sizeof(head));cnt=0;for(i=0;i<10005;i++)fa[i]=i;for(i=1;i<=m;i++){int u,v,w;scanf("%d%d%d",&u,&v,&w);add(u,v,w);add(v,u,w);int a=find(u);              int b=find(v);              if(a!=b){                  fa[b]=a;              } }for(i=1;i<=n;i++){//因为不一定是一棵树，所以不能只dfs（1,1,0,1） if(find(i)==i){dis[i]=0;dfs(i,1,0,1);}}for(int k=1;k<=16;k++){for(i=1;i<=n;i++){f[i][k]=f[f[i][k-1]][k-1];}}for(i=1;i<=c;i++){int u,v;scanf("%d%d",&u,&v);if(find(u)!=find(v))printf("Not connected\n");else{int ls=lca(u,v);printf("%d\n",dis[u]+dis[v]-2*dis[ls]);}}}return 0;}

下面是AC代码，别人地方拿的（http://www.cnblogs.com/pealicx/p/6396961.html）

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int maxn = 10050;int N, M, C;struct node{    int id, next, len;} E[maxn << 1];int head[maxn << 1], num;void initlist(){    memset(head, -1, sizeof(head));    num = 0;}void adde(int u, int v, int len){    E[num].id = u;    E[num].len = len;    E[num].next = head[v];    head[v] = num++;}//----------------------------------------邻接表int fa[maxn<<1];void initfa(){    for(int i = 0; i <= N; i++)        fa[i] = i;}int Find(int id){    if(id == fa[id]) return id;    else return fa[id] = Find(fa[id]);}void addu(int u, int v){    int x = Find(u);    int y = Find(v);    if(x != y)    fa[x] = y;}//----------------------------------------并查集int p[16][maxn], dep[maxn], dis[maxn], vis[maxn];void DFS(int u, int FA){    vis[u] = 1;    for(int l = head[u]; l != -1; l = E[l].next)    {        int id = E[l].id;        if(id == FA||vis[id]) continue;        dep[id] = dep[u] + 1;        dis[id] = dis[u] + E[l].len;        p[0][id] = u;        DFS(id, u);    }}void initlca(){    memset(p, -1, sizeof(p));    memset(dep,0,sizeof(dep));    memset(dis, 0, sizeof(dis));    memset(vis, 0, sizeof(vis));    for(int i = 1; i <= N; i++)    {        if(!vis[i])            DFS(i, -1);    }    for(int k = 0; k + 1 <= 15; k++)        for(int u = 1; u <= N; u++)        {            if(p[k][u] < 0) p[k + 1][u] = -1;            else                p[k + 1][u] = p[k][p[k][u]];        }}int LCA(int u, int v){    if(dep[u] > dep[v]) swap(u, v);    for(int k = 0; k <= 15; k++)    {        if((dep[v] - dep[u]) >> k & 1)            v = p[k][v];    }    if(u == v) return u;    for(int k = 15; k >= 0; k--)    {        if(p[k][u] != p[k][v])        {            u = p[k][u];            v = p[k][v];        }    }    return p[0][u];}//----------------------------------------LCAint main (){    while(~scanf("%d%d%d", &N, &M, &C))    {        initlist();        initfa();        int u, v, ds;        for(int i = 1; i <= M; i++)        {            scanf("%d%d%d", &u, &v, &ds);            adde(u, v, ds);            adde(v, u, ds);            addu(u, v);        }        initlca();        for(int i=1;i<=C;i++)        {            scanf("%d%d",&u,&v);            int x=Find(u);            int y=Find(v);            if(x==y)            {                printf("%d\n",dis[u]+dis[v]-2*dis[LCA(u,v)]);            }            else                printf("Not connected\n");        }    }    return 0;}