BZOJ3551 ONTAK2010Peaks加强版（kruskal重构树+dfs序+主席树）

　　kruskal重构树本质就是给并查集显式建树来替代可持久化并查集。将边按困难度从小到大排序后建出该树，按dfs序建主席树即可。查询时跳到深度最浅的满足在该重要度下已被合并的点，在子树内查询第k大。

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
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=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
#define N 200010
#define M 500010
int n,m,q,a[N],root[N],value[N],fa[N],p[N],size[N],dfn[N],id[N],f[N][19],lastans,tot,cnt=0,t=0;
struct data
{
    int x,y,z;
    bool operator <(const data&a) const
    {
        return z<a.z;
    }
}e[M];
struct data2{int to,nxt;
}edge[N];
struct data3{int l,r,x;
}tree[N<<5];
int find(int x){return fa[x]==x?x:fa[x]=find(fa[x]);}
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
void dfs(int k)
{
    size[k]=1;dfn[++cnt]=k;id[k]=cnt;
    for (int i=p[k];i;i=edge[i].nxt)
    {
        dfs(edge[i].to);
        size[k]+=size[edge[i].to];
    }
}
void ins(int &k,int l,int r,int x)
{
    tree[++cnt]=tree[k],k=cnt;tree[k].x++;
    if (l==r) return;
    int mid=l+r>>1;
    if (x<=mid) ins(tree[k].l,l,mid,x);
    else ins(tree[k].r,mid+1,r,x);
}
int query(int x,int y,int l,int r,int p)
{
    if (!y) return -1;
    if (l==r) return p<=tree[y].x-tree[x].x?l:-1;
    int mid=l+r>>1;
    if (p<=tree[tree[y].r].x-tree[tree[x].r].x) return query(tree[x].r,tree[y].r,mid+1,r,p);
    else return query(tree[x].l,tree[y].l,l,mid,p-tree[tree[y].r].x+tree[tree[x].r].x);
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("bzoj3551.in","r",stdin);
    freopen("bzoj3551.out","w",stdout);
    const char LL[]="%I64d
";
#else
    const char LL[]="%lld
";
#endif
    n=read(),m=read(),q=read();
    for (int i=1;i<=n;i++) a[i]=read();
    for (int i=1;i<=m;i++) e[i].x=read(),e[i].y=read(),e[i].z=read();
    sort(e+1,e+m+1);
    for (int i=1;i<=n*2;i++) fa[i]=i;tot=n;
    for (int i=1;i<=m;i++)
    if (find(e[i].x)!=find(e[i].y))
    {
        value[++tot]=e[i].z;
        addedge(tot,find(e[i].x)),addedge(tot,find(e[i].y));
        f[find(e[i].x)][0]=tot,f[find(e[i].y)][0]=tot;
        fa[find(e[i].x)]=tot,fa[find(e[i].y)]=tot;
    }
    for (int i=1;i<=tot;i++) if (!f[i][0]) f[i][0]=i;
    for (int j=1;j<=18;j++)
        for (int i=1;i<=tot;i++)
        f[i][j]=f[f[i][j-1]][j-1];
    for (int i=1;i<=tot;i++)
    if (f[i][0]==i) dfs(i);
    cnt=0;
    for (int i=1;i<=tot;i++)
    {
        root[i]=root[i-1];
        ins(root[i],-1,1E9,dfn[i]>n?-1:a[dfn[i]]);
    }
    while (q--)
    {
        int x=read(),y=read(),z=read();
        if (~lastans) x^=lastans,y^=lastans,z^=lastans;
        for (int j=18;~j;j--) if (value[f[x][j]]<=y) x=f[x][j];
        lastans=query(root[id[x]-1],root[id[x]+size[x]-1],-1,1E9,z);
        printf("%d
",lastans);
    }
    return 0;
}