Submission #329485

#	Time	Username	Problem	Language	Result	Execution time	Memory
329485		Kuuhaku	Aesthetic (NOI20_aesthetic)	C++17	100 / 100	723 ms	49900 KiB

Aesthetic

//Nov21-2020
#define tasknames "aesthetic"
#include <iostream>
#include <stdio.h>
#include <vector>
#include <queue>
#include <stack>
using namespace std;
const int maxn=3e5+2;
int n, m, x[maxn], y[maxn], c[maxn], maxc[maxn], Time=0, num[maxn], low[maxn];
long long d[2][maxn];
bool ch[2][maxn], kt;
stack<int> st;

struct T
{
    int v, w, id;
};
vector<T> a[maxn];

void Dijkstra(int s,int h)
{
    priority_queue<pair<long long,int>> pq;
    for(int i=1;i<=n;i++)
        d[h][i]=1e18;
    d[h][s]=0;
    pq.push({0,s});
    while(!pq.empty())
    {
        auto u=pq.top();
        pq.pop();
        u.first=-u.first;
        if(u.first!=d[h][u.second])
            continue;
        for(T v:a[u.second])
            if(d[h][v.v]>u.first+v.w)
            {
                d[h][v.v]=u.first+v.w;
                pq.push({-d[h][v.v],v.v});
            }
    }
}

void Enter()
{
    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int u, v, w;
        cin>>u>>v>>w;
        a[u].push_back({v,w,i});
        a[v].push_back({u,w,i});
        x[i]=u;y[i]=v;c[i]=w;
    }
    for(int i=m;i>0;i--)
        maxc[i]=max(maxc[i+1],c[i+1]);
    Dijkstra(1,0);
    Dijkstra(n,1);
}

void Tarjan(int u,int par)
{
    num[u]=low[u]=++Time;
    for(T v:a[u])
    {
        if(!ch[0][v.id])continue;
        if(num[v.v])
        {
            if(v.v!=par)
                low[u]=min(low[u],num[v.v]);
        }
        else
        {
            Tarjan(v.v,u);
            if(low[v.v]>num[u]&&num[n]>=num[v.v]&&ch[1][v.id])
                kt=true;
            else low[u]=min(low[u],low[v.v]);
        }
    }
}

bool Check(long long mid)
{
    for(int i=1;i<=m;i++)
    {
        long long dist=min(d[0][x[i]]+d[1][y[i]],d[1][x[i]]+d[0][y[i]])+c[i];
        ch[0][i]=(dist<=mid);
        ch[1][i]=((dist+maxc[i])>mid);
    }
    fill_n(num,n+1,0);
    fill_n(low,n+1,1e9);
    Time=0;kt=false;
    Tarjan(1,0);
    if(kt||num[n]==0)return true;
    return false;
}

void Solve()
{
    long long l=d[0][n], r=d[0][n]+maxc[1], mid;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(Check(mid))
            l=mid+1;
        else r=mid-1;
    }
    cout<<l;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    Enter();
    Solve();
}

• Subtask 1: 5 / 5
• Subtask 2: 8 / 8
• Subtask 3: 7 / 7
• Subtask 4: 15 / 15
• Subtask 5: 16 / 16
• Subtask 6: 22 / 22
• Subtask 7: 27 / 27