Roads in the Kingdom CodeForces - 835F (直径)

大意: 给定一个基环树, 求删除一条环上的边使得直径最小.

直径分两种情况

  • 环上点延伸的树内的直径
  • 两个环上点的树内深度最大的点匹配

第一种情况直接树形dp求一下, 第二种情况枚举删除的环边, 线段树维护一下即可.

 

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl '\n'
#define DB(a) ({REP(__i,1,n) cout< pii;
const int P = 1e9+7, INF = 0x3f3f3f3f;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
inline int rd() {int x=0;char p=getchar();while(p<'0'||p>'9')p=getchar();while(p>='0'&&p<='9')x=x*10+p-'0',p=getchar();return x;}
//head



const int N = 1e6+10;
int n,dep[N],vis[N];
struct _ {int to,w;} fa[N];
vector<_> g[N];
int a[N], v[N], top;
ll mx[N], b[N], sum[N], ans, ans2;
struct node {
	ll m1,m2,v;
	node operator + (const node &rhs) const {
		node ret;
		ret.m1=max(m1,rhs.m1);
		ret.m2=max(m2,rhs.m2);
		ret.v=max(v,rhs.v);
		ret.v=max(ret.v,m2+rhs.m1);
		return ret;
	}
} tr[N<<2];
 
void get(int x, int y) {
    if (dep[x]=qr) return qry(ls,ql,qr);
	if (mid 
 

 

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