P2680 运输计划

P2680 运输计划

首先看到最大的最小要想到二分

之后考虑check..

我们将道路长度>mid的标记,找出被所有道路标记的边,去掉其中最大的,之后再和mid比较即可.

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#include<bits/stdc++.h>
#define ll long long
#define max(a,b) a>b?a:b
#define re register
using namespace std;
const int N=3e5+10;
int n,m,link[N],tot,d[N],c[N],cnt,ans,f[N][25],deep[N],dire[N];
struct edge{int y,v,next;}a[N<<1];
struct data{int x,y,v;}b[N];
vector<int>v;
char buf[1<<15],*fs,*ft;
inline char getc()
{
    return (fs==ft&&(ft=(fs=buf)+fread(buf,1,1<<15,stdin),fs==ft))?0:*fs++;
}
inline int read()
{
    int x=0,ff=1;
    char ch=getc();
    while(!isdigit(ch)) {if(ch=='-') ff=-1;ch=getc();}
    while(isdigit(ch)) {x=(x<<1)+(x<<3)+(ch^48);ch=getc();}
    return x*ff;
}
inline void add(int x,int y,int v)
{
    a[++tot].y=y;a[tot].v=v;a[tot].next=link[x];link[x]=tot;
    a[++tot].y=x;a[tot].v=v;a[tot].next=link[y];link[y]=tot;
}
inline void bfs()
{
    queue<int>q;q.push(1);
    memset(deep,0,sizeof(deep));
    deep[1]=1;
    while(!q.empty())
    {
        int x=q.front();q.pop();
        for(re int i=link[x];i;i=a[i].next)
        {
            int y=a[i].y;
            if(deep[y]) continue;
            dire[y]=i;
            deep[y]=deep[x]+1;
            q.push(y);
            f[y][0]=x;
            for(re int j=1;j<21;++j) f[y][j]=f[f[y][j-1]][j-1];
        } 
    }
}
inline int lca(int a,int b)
{
    if(deep[a]>deep[b]) swap(a,b);
    for(re int i=20;i>-1;--i)
        if(deep[f[b][i]]>=deep[a]) b=f[b][i];
    if(a==b) return a;
    for(re int i=20;i>-1;--i)
        if(f[b][i]!=f[a][i]) a=f[a][i],b=f[b][i];
    return f[a][0];
}
inline void dfs(int x)
{
    for(re int i=link[x];i;i=a[i].next)
    {
        int y=a[i].y;
        if(y==f[x][0]) continue;
        d[y]=d[x]+a[i].v;
        dfs(y);
    }
}
inline void dfs1(int x)
{
    for(re int i=link[x];i;i=a[i].next)
    {
        int y=a[i].y;
        if(y==f[x][0]) continue;
        dfs1(y);
        c[x]+=c[y];
    }
    if(c[x]==cnt) ans=max(ans,a[dire[x]].v);
}
inline bool check(int mid)
{
    cnt=0;v.clear();
    memset(c,0,sizeof(c));
    for(re int i=1;i<m+1;++i) 
    {
        if(b[i].v>mid)
        {
            cnt++;
            c[b[i].x]++;
            c[b[i].y]++;
            c[lca(b[i].x,b[i].y)]-=2;
            v.push_back(i);
        }
    }
    if(!cnt) return true;
    ans=0;dfs1(1);
    if(!ans) return false;
    int len=v.size();
    for(int i=0;i<len;++i) if(b[v[i]].v-ans>mid) return false;
    return true;
}
int main()
{
    //freopen("1.in","r",stdin);
    n=read();m=read();
    for(re int i=1;i<n;++i)
    {
        int x=read(),y=read(),v=read();
        add(x,y,v);
    }
    bfs();dfs(1);
    for(re int i=1;i<m+1;++i) 
    {
        b[i].x=read();
        b[i].y=read();
        b[i].v=d[b[i].x]+d[b[i].y]-2*d[lca(b[i].x,b[i].y)];
    }
    int l=0,r=0;
    for(re int i=1;i<n+1;++i) r=max(r,d[i]);
    r*=2;
    while(l<r)
    {
        int mid=l+r>>1;
        if(check(mid)) r=mid;
        else           l=mid+1;
    }
    printf("%d",l);
    return 0;
}