【LCA模板題】POJ 1330

RMQ版

#define N 10010
struct edge{
    int v;
    int next;
}e[2*N];
int ecnt;
int head[N];
bool vis[N];
int n;//點數
int R[N];//第一次出現i點下標
int p[N*2];//記錄路徑點編號
//int dis[N];//與根的距離
int dep[2*N];//深度
int dp[20][2*N];//從j開始長度爲2^i路徑的最近公共祖先下標
int num;
void init(){
    memset(head,-1,sizeof(head));
    memset(R,-1,sizeof(R));
    memset(vis,0,sizeof(vis));
    ecnt=0;
}
void add(int u,int v){
    e[ecnt].v = v;
    e[ecnt].next = head[u];
    head[u] = ecnt++;
    e[ecnt].v = u;
    e[ecnt].next = head[v];
    head[v] = ecnt++;
}
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]){
            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編號
    //if(R[u]>=R[v])swap(u,v);
    int s = R[u],t = R[v];
    if(s>t)swap(s,t);
    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 du[N];
int main(){
    int t;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        int i,j;
        init();
        for(i=0;i<=n;i++)du[i] = 0;
        for(i=1;i<n;i++){
            int a,b;
            scanf("%d%d",&a,&b);
            du[b] = 1;
            add(a,b);
        }
        int root=1;
        for(i=1;i<=n;i++){
            if(!du[i]){
                root = i;
                break;
            }
        }
        num = 0;
        dep[root] = 0;
        dfs(root,0);
        init_rmq();
        int a,b;
        scanf("%d%d",&a,&b);
        printf("%d\n",rmq(a,b));
    }
    return 0;
}