【LCA转RMQ求树上任意两点最短路】HDU 2874

#define N 10010
struct edge{
int v;
int len;
int next;
}e[2*N];
int ecnt;
int head
;
bool vis
;
int n;//点数
int R
;//第一次出现i点下标
int p[N*2];//记录路径点编号
int dis
;//与根的距离
int dep[2*N];//深度
int dp[20][2*N];//从j开始长度为2^i路径的最近公共祖先下标，这里这里！！！第二维要2倍大小！！
int num;
int fa
;
void init(){
memset(head,-1,sizeof(head));
memset(R,-1,sizeof(R));
memset(vis,0,sizeof(vis));
for(int i=1;i<=n;i++)fa[i] = i;
ecnt=0;
}
void add(int u,int v,int len){
e[ecnt].v = v;
e[ecnt].len = len;
e[ecnt].next = head[u];
head[u] = ecnt++;

e[ecnt].v = u;
e[ecnt].len = len;
e[ecnt].next = head[v];
head[v] = ecnt++;
}
int find(int x){
if(fa[x] != x)
fa[x] = find(fa[x]);
return fa[x];
}
void uni(int u,int v){
int a = find(u);
int b = find(v);
if(a == b)return ;
fa[a] = b;
}
void dfs(int u,int depth){
vis[u] = 1;
p[++num] = u;
dep[num] = depth;
for(int i=head[u];i!=-1;i=e[i].next){
int v = e[i].v;
if(!vis[v]){
dis[v] = dis[u]+e[i].len;
dfs(v,depth+1);
p[++num] = u;
dep[num] = depth;
}
}
}
void init_rmq(){
int i,j;
for(i=1;i<=num;i++){
if(R[p[i]] == -1){
R[p[i]] = i;
}
}
for(i=1;i<=num;i++){
dp[0][i] = i;
}
int t = (int)(log(num*1.0)/log(2.0));
for(i=1;i<=t;i++){
for(j=1;j+(1<<(i-1))<=num;j++){
int a = dp[i-1][j],b = dp[i-1][j+(1<<(i-1))];
if(dep[a]<=dep[b]){
dp[i][j] = a;
} else dp[i][j] = b;
}
}
}
int rmq(int u,int v){//返回最近公共祖先的编号
if(R[u]>=R[v])swap(u,v);
int s = R[u],t = R[v];
int k = (int)(log((t-s+1)*1.0)/log(2.0));
int a = dp[k][s],b = dp[k][t-(1<<k)+1];
if(dep[a]<=dep[b])return p[a];
else return p[b];
}
int main(){
int m,c;
while(scanf("%d%d%d",&n,&m,&c) != -1){
int i,j;
init();
int x,y,z;
while(m--){
scanf("%d%d%d",&x,&y,&z);
add(x,y,z);
uni(x,y);
}
for(i=1;i<=n;i++){
if(fa[i] == i){
add(i,0,0);//添加虚根0把森林变成树
}
}
num = 0;
dis[0] = dep[0] = 0;
dfs(0,0);
init_rmq();
while(c--){
scanf("%d%d",&x,&y);
int f = rmq(x,y);
if(!f)puts("Not connected");
else printf("%d\n",dis[x]+dis[y]-2*dis[f]);
}
}
return 0;
}