P3379 板子 倍增和tarjan求Lca

· · 个人记录

倍增：

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
int n,m,s;
int head[N],nxt[N],to[N],cnt;
int deep[N],fa[N][25];
void add(int u,int v){
    nxt[++cnt]=head[u];
    head[u]=cnt;
    to[cnt]=v;
    return ;
}
void dfs(int x,int father){
    deep[x]=deep[father]+1;
    fa[x][0]=father;
    for(int i=1;(1<<i)<=deep[x];i++)    fa[x][i]=fa[fa[x][i-1]][i-1];   //(1<<i)<=deep[x]
    for(int i=head[x];i;i=nxt[i])   if(to[i]!=father) dfs(to[i],x);     //if(to[i]!=father)
}
int lca(int x,int y){
    if(deep[x]<deep[y]) swap(x,y);
    for(int i=24;i>=0;i--)  if(deep[x]-(1<<i)>=deep[y]) x=fa[x][i];     //(deep[x]-(1<<i) >= deep[y])
    if(x==y) return x;
    for(int i=24;i>=0;i--)  if(fa[x][i]!=fa[y][i]) x=fa[x][i],y=fa[y][i];
    return fa[x][0];
}
int main(){
    scanf("%d%d%d",&n,&m,&s);
    int a,b;
    for(int i=1;i<n;i++){
        scanf("%d%d",&a,&b);
        add(a,b),add(b,a);
    }   
    dfs(s,0);
    for(int i=1;i<=m;i++){
        scanf("%d%d",&a,&b);
        printf("%d\n",lca(a,b));
    }
    return 0;
}

tarjan：

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
int n,m,s;
int head[N],nxt[N],to[N],cnt;
int head_query[N],nxt_query[N],to_query[N],num_query[N],cnt_query;
int vis[N],fa[N];
int ans[N];
inline int read(){
    register int x=0;register char s=getchar();
    while(s<'0'||s>'9') s=getchar();
    while(s>='0'&&s<='9') x=(x<<1)+(x<<3)+(s^48),s=getchar();
    return x;
}
void add(int u,int v){nxt[++cnt]=head[u],head[u]=cnt,to[cnt]=v;}
void add_query(int u,int v,int num){
    nxt_query[++cnt_query]=head_query[u];
    head_query[u]=cnt_query;
    to_query[cnt_query]=v;
    num_query[cnt_query]=num;
}
int find(int a){return fa[a]==a?a:fa[a]=find(fa[a]);}
void tarjan(int root){
    vis[root]=1;
    for(register int i=head[root];i;i=nxt[i]){
        register int v=to[i];
        if(!vis[v]){
            tarjan(v);
            fa[v]=root;
        }
    }
    for(register int i=head_query[root];i;i=nxt_query[i]){
        register int v=to_query[i];
        if(vis[v])  ans[num_query[i]]=find(v);
    }
}
signed  main(){
    n=read(),m=read(),s=read();
    register int a,b;
    for(register int i=1;i<n;++i){
        fa[i]=i;
        a=read(),b=read();
        add(a,b),add(b,a);
    }
    fa[n]=n;

    for(register int i=1;i<=m;++i){
        a=read(),b=read();
        add_query(a,b,i),add_query(b,a,i);
    }

    tarjan(s);
    for(register int i=1;i<=m;++i) printf("%d\n",ans[i]);
    return 0;
}