BZOJ1095: [ZJOI2007]Hide 捉迷藏

题目：http://www.lydsy.com/JudgeOnline/problem.php?id=1095

括号序列。。

orz岛娘http://www.shuizilong.com/house/archives/bzoj-1095-zjoi2007hide-%E6%8D%89%E8%BF%B7%E8%97%8F/

#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdio>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define maxn 200500
#define inf int(1e9)
#define ll long long
#define mm 1000000007
using namespace std;
int head[maxn],dfn[maxn*3],a[maxn*3],c[maxn],tot,n,q;
struct data{int obj,pre;
}e[maxn*2];
struct seg{
    int l,r,l1,l2,r1,r2,c1,c2,s;
    void ini(int x){
        l=r=x;
        if (a[x]==-2) c2=1;
        if (a[x]==-5) c1=1;
        if (a[x]>0&&c[a[x]]==1) l1=l2=r1=r2=0;
        else l1=l2=r1=r2=-inf;
    }
} t[maxn*3*4];
int read(){
    int x=0,f=1; char ch=getchar();
    while (!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}
    while (isdigit(ch)) {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}
void insert(int x,int y){
    e[++tot].obj=y; e[tot].pre=head[x]; head[x]=tot;
}
void dfs(int u,int f){
    a[++tot]=-2;
    a[++tot]=u; dfn[u]=tot;
    for (int j=head[u];j;j=e[j].pre){
        int v=e[j].obj;
        if (v!=f) dfs(v,u);
    }
    a[++tot]=-5;
}
inline seg merge(seg s1,seg s2){
    seg s;
    s.l=s1.l,s.r=s2.r;
    int a=s1.c1,b=s1.c2,c=s2.c1,d=s2.c2;
    if (c>b) s.c1=a+c-b,s.c2=d;
    if (c<=b) s.c1=a,s.c2=d+b-c;
    s.s=max(s1.s,s2.s);
    s.s=max(s.s,s1.r1+s2.l2);
    s.s=max(s.s,s1.r2+s2.l1);
    s.r1=max(s2.r1,max(s1.r1-c+d,s1.r2+c+d));
    s.r2=max(s2.r2,s1.r2+c-d);
    s.l1=max(s1.l1,max(s2.l1+a-b,s2.l2+a+b));
    s.l2=max(s1.l2,s2.l2-a+b);
    return s;
}
void change(int i,int x){
    int l=t[i].l,r=t[i].r,mid=(l+r)/2;
    if (l==r) {t[i].ini(x); return;}
    if (x<=mid) change(i*2,x);
    else change(i*2+1,x);
    t[i]=merge(t[i*2],t[i*2+1]);
}
void build(int i,int l,int r){
    if (l==r){
        t[i].l=l; t[i].r=r; t[i].ini(l);
        return;
    }
    int mid=(l+r)/2;
    build(i*2,l,mid); build(i*2+1,mid+1,r);
    t[i]=merge(t[i*2],t[i*2+1]);
}
int main(){
    n=read();
    int black=0;
    rep(i,1,n) c[i]=1,black++;
    rep(i,1,n-1){
        int x=read(),y=read();
        insert(x,y); insert(y,x);
    }
    dfs(1,0);
    build(1,1,tot);
    q=read();
    char ch[2]; 
    rep(i,1,q){
        scanf("%s",ch);
        if (ch[0]=='G'){
            if (!black) puts("-1"); 
            else if (black==1) puts("0");
            else printf("%d
",t[1].s);
        }
        else {
            int x=read(); 
            if (c[x]) black--; else black++; c[x]^=1;
            change(1,dfn[x]);
        }
    }
    return 0;
}