LibreOJ 2179 「BJOI2017」树的难题

发表于 | 分类于 | 19

显而易见地，点分治然后暴力维护两棵线段树（颜色相同 / 不同）算贡献，算完之后合并这两棵线段树再看下一种颜色（

代码： 

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#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
const int N = 2e5;
int n,m,l,r;
int a[N + 5],v[N + 5];
int to[(N << 1) + 5],pre[(N << 1) + 5],val[(N << 1) + 5],first[N + 5];
inline void add(int u,int v,int w)
{
    static int tot = 0;
    to[++tot] = v,val[tot] = w,pre[tot] = first[u],first[u] = tot;
}
namespace SEG
{
    struct node
    {
        int max;
        int ls,rs;
    } seg[(N << 3) + 10];
    int rt[N + 5];
    int init()
    {
        seg[0].max = -2e9;
        return 0;
    }
    int Init = init(),tot;
    void insert(int x,int k,int &p,int tl,int tr)
    {
        !p && (seg[p = ++tot].max = -2e9,seg[p].ls = seg[p].rs = 0),seg[p].max = max(seg[p].max,k);
        if(tl == tr)
            return ;
        int mid = tl + tr >> 1;
        x <= mid ? insert(x,k,seg[p].ls,tl,mid) : insert(x,k,seg[p].rs,mid + 1,tr);
    }
    int query(int l,int r,int p,int tl,int tr)
    {
        if(!p || (l <= tl && tr <= r))
            return seg[p].max;
        int mid = tl + tr >> 1;
        int ret = -2e9;
        l <= mid && (ret = max(ret,query(l,r,seg[p].ls,tl,mid)));
        r > mid && (ret = max(ret,query(l,r,seg[p].rs,mid + 1,tr)));
        return ret;
    }
    int merge(int p,int q)
    {
        if(!p || !q)
            return p | q;
        seg[p].max = max(seg[p].max,seg[q].max),
        seg[p].ls = merge(seg[p].ls,seg[q].ls),seg[p].rs = merge(seg[p].rs,seg[q].rs);
        return p;
    }
}
namespace LIS
{
    int pre[N + 5],first[N + 5];
    inline void add(int p,int v)
    {
        pre[p] = first[v],first[v] = p;
    }
}
int vis[N + 5],sum,sz[N + 5],max_part[N + 5],cur[N + 5],rt;
int    done[N + 5];
int dis[N + 5],dep[N + 5],fa[N + 5];
int col[N + 5],len;
int ans;
void get_rt(int p)
{
    done[p] = fa[p] = 0;
    for(int flag;;)
    {
        flag = 0;
        if(!done[p])
            sz[p] = 1,max_part[p] = 0,cur[p] = first[p],done[p] = 1;
        for(register int i = cur[p];i;i = pre[i])
        {
            cur[p] = pre[i];
            if((to[i] ^ fa[p]) && !vis[to[i]])
            {
                done[to[i]] = 0,fa[to[i]] = p,p = to[i],flag = 1;
                break;
            }
        }
        if(!flag)
        {
            max_part[p] = max(max_part[p],sum - sz[p]);
            max_part[p] < max_part[rt] && (rt = p);
            if(fa[p])
            {
                sz[fa[p]] += sz[p],max_part[fa[p]] = max(max_part[fa[p]],sz[p]);
                p = fa[p];
            }
            else
                break;
        }
    }
    /*sz[p] = 1,max_part[p] = 0;
    for(register int i = first[p];i;i = pre[i])
        if((to[i] ^ fa) && !vis[to[i]])
            get_rt(to[i],p),sz[p] += sz[to[i]],max_part[p] = max(max_part[p],sz[to[i]]);
    max_part[p] = max(max_part[p],sum - sz[p]);
    max_part[p] < max_part[rt] && (rt = p);*/
}
void get_dis(int p)
{
    done[p] = fa[p] = 0;
    for(int flag;;)
    {
        flag = 0;
        if(!done[p])
            cur[p] = first[p],done[p] = 1;
        for(register int i = cur[p];i;i = pre[i])
        {
            cur[p] = pre[i];
            if((to[i] ^ fa[p]) && !vis[to[i]])
            {
                done[to[i]] = 0,fa[to[i]] = p,dep[to[i]] = dep[p] + 1,v[to[i]] = val[i],dis[to[i]] = dis[p] + (v[p] != v[to[i]]) * a[v[to[i]]],p = to[i],flag = 1;
                break;
            }
        }
        if(!flag)
            if(fa[p])
                p = fa[p];
            else
                break;
    }
    /*for(register int i = first[p];i;i = pre[i])
        if((to[i] ^ fa) && !vis[to[i]])
            dep[to[i]] = dep[p] + 1,v[to[i]] = val[i],dis[to[i]] = dis[p] + (v[p] != v[to[i]]) * a[v[to[i]]],get_dis(to[i],p);*/
}
void calc(int p,int c)
{
    done[p] = fa[p] = 0;
    for(int flag;;)
    {
        flag = 0;
        if(!done[p])
        {
            cur[p] = first[p],done[p] = 1;
            if(dep[p] >= l && dep[p] <= r)
                ans = max(ans,dis[p]);
            int temp = SEG::query(max(l - dep[p],1),r - dep[p],SEG::rt[0],1,n);
            if(temp > -2e9)
                ans = max(ans,temp + dis[p]);
            temp = SEG::query(max(l - dep[p],1),r - dep[p],SEG::rt[c],1,n);
            if(temp > -2e9)
                ans = max(ans,temp + dis[p] - a[c]);
        }
        for(register int i = cur[p];i;i = pre[i])
        {
            cur[p] = pre[i];
            if((to[i] ^ fa[p]) && !vis[to[i]] && dep[to[i]] <= r)
            {
                done[to[i]] = 0,fa[to[i]] = p,p = to[i],flag = 1;
                break;
            }
        }
        if(!flag)
            if(fa[p])
                p = fa[p];
            else
                break;
    }
    /*if(dep[p] >= l && dep[p] <= r)
        ans = max(ans,dis[p]);
    if(dep[p] > r)
        return ;
    for(register int i = first[p];i;i = pre[i])
        if((to[i] ^ fa) && !vis[to[i]])
            calc(to[i],p,c);*/
}
void insert(int p,int c)
{
    done[p] = fa[p] = 0;
    for(int flag;;)
    {
        flag = 0;
        if(!done[p])
        {
            cur[p] = first[p],done[p] = 1;
            SEG::insert(dep[p],dis[p],SEG::rt[c],1,n);
        }
        for(register int i = cur[p];i;i = pre[i])
        {
            cur[p] = pre[i];
            if((to[i] ^ fa[p]) && !vis[to[i]] && dep[to[i]] <= r)
            {
                done[to[i]] = 0,fa[to[i]] = p,p = to[i],flag = 1;
                break;
            }
        }
        if(!flag)
            if(fa[p])
                p = fa[p];
            else
                break;
    }
    /*if(dep[p] > r)
        return ;
    SEG::insert(dep[p],dis[p],SEG::rt[c],1,n);
    for(register int i = first[p];i;i = pre[i])
        if((to[i] ^ fa) && !vis[to[i]])
            insert(to[i],p,c);*/
}
void solve(int p)
{
    vis[p] = 1,dep[p] = dis[p] = v[p] = 0,get_dis(p),len = 0;
    for(register int i = first[p];i;i = pre[i])
        if(!vis[to[i]])
            LIS::add(to[i],v[to[i]]),col[++len] = v[to[i]];
    sort(col + 1,col + len + 1),len = unique(col + 1,col + len + 1) - col - 1;
    for(register int ci = 1,c;ci <= len;++ci)
    {
        c = col[ci];
        for(register int i = LIS::first[c];i;i = LIS::pre[i])
            calc(i,c),insert(i,c);
        SEG::rt[0] = SEG::merge(SEG::rt[0],SEG::rt[c]),
        LIS::first[c] = SEG::rt[c] = 0;
    }
    SEG::tot = SEG::rt[0] = 0;
    for(register int i = first[p];i;i = pre[i])
        if(!vis[to[i]])
            rt = 0,sum = sz[to[i]],fa[to[i]] = p,get_rt(to[i]),solve(rt);
}
int main()
{
    max_part[0] = 0x3f3f3f3f,ans = -2e9;
    scanf("%d%d%d%d",&n,&m,&l,&r);
    for(register int i = 1;i <= m;++i)
        scanf("%d",a + i);
    int u,v,w;
    for(register int i = 2;i <= n;++i)
        scanf("%d%d%d",&u,&v,&w),add(u,v,w),add(v,u,w);
    vis[0] = 1,rt = 0,sum = n,get_rt(1),solve(rt);
    printf("%d\n",ans);
}

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