学习笔记::启发式合并

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 400010
int n,m,Q;
int size[N],fa[N],key[N],father[N],Rank[N],q[N];
int child[N][2];
int read()
{
    int x=0,f=1; char c=getchar();
    while(c<‘0‘||c>‘9‘) {if(c==‘-‘) f=-1; c=getchar(); }
    while(c>=‘0‘&&c<=‘9‘) {x*=10; x=x+c-‘0‘; c=getchar();}
    return x*f;
}
void update(int x)
{
    size[x]=size[child[x][0]]+size[child[x][1]]+1;
}
void zig(int x)
{
    int y=fa[x];
    fa[x]=fa[y]; child[fa[x]][child[fa[x]][1]==y]=x;
    child[y][0]=child[x][1]; fa[child[x][1]]=y;
    fa[y]=x; child[x][1]=y;
    update(y); update(x);
}
void zag(int x)
{
    int y=fa[x];
    fa[x]=fa[y]; child[fa[x]][child[fa[x]][1]==y]=x;
    child[y][1]=child[x][0]; fa[child[x][0]]=y;
    fa[y]=x; child[x][0]=y;
    update(y); update(x);
}
void splay(int x)
{
    while(fa[x])
    {
        int y=fa[x],z=fa[y];
        if(!z)
        {
            child[y][0]==x?zig(x):zag(x); break;
        }
        child[y][0]==x?zig(x):zag(x);
        child[z][0]==x?zig(x):zag(x);
    }
}
void insert(int x,int root)
{
    int y=root,last;
    while(y)
    {
        last=y;
        if(key[x]>key[y]) y=child[y][1];
        else y=child[y][0];
    }
    fa[x]=last;
    child[last][(key[x]>key[last])]=x;
    update(x); update(last);
    splay(x);
}
void merge(int x,int y)
{
    splay(x); splay(y);
    if(size[x]>size[y]) swap(x,y);
    int l=1,r=0;
    q[++r]=x;
    while(l<=r)
    {
        int u=q[l++];
        if(child[u][0]) q[++r]=child[u][0];
        if(child[u][1]) q[++r]=child[u][1];
    }
    q[0]=y;
    for(int i=1;i<=r;i++) insert(q[i],q[i-1]);
}
int findkth(int x,int k)
{
    if(size[child[x][0]]==k-1) return x;
    if(size[child[x][0]]+1>k) return findkth(child[x][0],k);
    else return findkth(child[x][1],k-size[child[x][0]]-1);
}
int find(int x)
{
    return father[x]==x?father[x]:find(father[x]);
}
void connect(int x,int y)
{
    int a=find(x),b=find(y);
    if(a==b) return;
    if(Rank[a]>=Rank[b])
    {
        Rank[a]+=Rank[b];
        father[b]=a;
    }
    else
    {
        Rank[b]+=Rank[a];
        father[a]=b;
    }
}
void link(int x,int y)
{
    if(find(x)==find(y)) return;
    merge(x,y);
    connect(x,y);
}
void query(int x,int k)
{
    splay(x);
    if(size[x]<k) 
    {
        printf("-1\n");
        return;
    }
    printf("%d\n",findkth(x,k));
}
int main()
{
    n=read(); m=read();
    for(int i=1;i<=n;i++)
    {
        key[i]=read();
        father[i]=i;
        Rank[i]=size[i]=1;
    }
    for(int i=1;i<=m;i++) 
    {
        int u,v; u=read(); v=read();
        if(u==0||v==0) continue;
        link(u,v);
    }
    Q=read();
    while(Q--)
    {
        char s[10]; int a,b; scanf("%s",s);
        a=read(); b=read();
        if(a==0||b==0) continue;
        if(s[0]==‘B‘) link(a,b);
        if(s[0]==‘Q‘) query(a,b);
    }
    return 0;
}