Submission #274281

#	Time	Username	Problem	Language	Result	Execution time	Memory
274281		gs18115	Mountains and Valleys (CCO20_day1problem3)	C++14	2 / 25	44 ms	40448 KiB

Main

#include<iostream>
#include<vector>
#include<algorithm>
#define ep emplace
#define eb emplace_back
#define fi first
#define se second
#define all(x) (x).begin(),(x).end()
using namespace std;
typedef long long ll;
typedef pair<int,int>pi;
typedef pair<ll,ll>pl;
const int inf=1e9+7;
const ll INF=1e18;
struct max3
{
    int a,b,c;
    max3(){a=b=c=0;}
    inline void upd(int x)
    {
        if(x>a)
            c=b,b=a,a=x;
        else if(x>b)
            c=b,b=x;
        else if(x>c)
            c=x;
        return;
    }
    inline int get()
    {
        return a;
    }
    inline int get(int x)
    {
        return x==a?b:a;
    }
    inline int get(int x,int y)
    {
        if(x<y)
            swap(x,y);
        return x==a?(y==b?c:b):(y==a?b:a);
    }
};
struct max4
{
    int a,b,c,d;
    max4(){a=b=c=d=0;}
    inline void upd(int x)
    {
        if(x>a)
            d=c,c=b,b=a,a=x;
        else if(x>b)
            d=c,c=b,b=x;
        else if(x>c)
            d=c,c=x;
        else if(x>d)
            d=x;
        return;
    }
    inline int get()
    {
        return a;
    }
    inline int get(int x)
    {
        return x==a?b:a;
    }
    inline int get(int x,int y)
    {
        if(x<y)
            swap(x,y);
        return x==a?(y==b?c:b):(y==a?b:a);
    }
};
vector<int>adj[500010];
int depth[500010];
void ddfs(int x,int p)
{
    depth[x]=depth[p]+1;
    for(int&t:adj[x])
        if(t!=p)
            ddfs(t,x);
    return;
}
int dep[500010];
int spa[500010][19];
inline int kpa(int x,int k)
{
    for(;k>0;k^=k&-k)
        x=spa[x][__builtin_ctz(k)];
    return x;
}
inline int lca(int x,int y)
{
    if(dep[x]>dep[y])
        x=kpa(x,dep[x]-dep[y]);
    else
        y=kpa(y,dep[y]-dep[x]);
    if(x==y)
        return x;
    for(int i=19;i-->0;)
        if(spa[x][i]!=spa[y][i])
            x=spa[x][i],y=spa[y][i];
    return spa[x][0];
}
max3 dp1[500010],dp2[500010];
int dpex[500010],dpe[500010];
int spd[500010][19];
inline int dpth(int x,int k)
{
    int ret=max({dp2[x].a,dp1[x].a+dp1[x].get(dp1[x].a)});
    while(k>0)
    {
        int i=__builtin_ctz(k);
        k^=k&-k;
        ret=max(ret,spd[x][i]);
        x=spa[x][i];
    }
    return ret;
}
int cm[500010][19];
pi cut[500010][19];
inline pi pth(int x,int k)
{
    pi ret;
    ret.fi=dp1[x].a;
    ret.se=-inf;
    int len=0;
    while(k>0)
    {
        int i=__builtin_ctz(k);
        k^=k&-k;
        ret.se=max({cm[x][i]+len,ret.se+(1<<i),ret.fi+cut[x][i].se});
        ret.fi=max(ret.fi,cut[x][i].fi+len);
        len+=1<<i;
        x=spa[x][i];
    }
    return ret;
}
max4 dp3[500010];
max3 dp4[500010];
void sdfs(int x,int p)
{
    spa[x][0]=p;
    for(int i=0;i<18;i++)
        spa[x][i+1]=spa[spa[x][i]][i];
    dep[x]=dep[p]+1;
    for(int&t:adj[x])
        if(t!=p)
            sdfs(t,x),dp1[x].upd(dp1[t].a+1),
            dp2[x].upd(max(dp2[t].a,dp1[t].a+dp1[t].get(dp1[t].a)));
    dp3[x].a=dp1[x].a;
    dp3[x].b=dp1[x].b;
    dp3[x].c=dp1[x].c;
    dp4[x]=dp2[x];
    return;
}
void dfs2(int x,int p)
{
    spd[x][0]=dpex[x];
    cm[x][0]=dpe[x];
    cut[x][0].fi=dpe[x]+1;
    cut[x][0].se=dpe[x];
    for(int i=0,y=x;i<18;y=spa[y][i++])
    {
        if(spa[x][i]==0)
            break;
        spd[x][i+1]=max(spd[x][i],spd[spa[x][i]][i]);
        cm[x][i+1]=max({cm[x][i]+(1<<i),cm[spa[x][i]][i]+(1<<i),
        cut[x][i].fi+cut[spa[x][i]][i].se});
        cut[x][i+1].fi=max(cut[x][i].fi,cut[spa[x][i]][i].fi+(1<<i));
        cut[x][i+1].se=max(cut[spa[x][i]][i].se,cut[x][i].se+(1<<i));
    }
    for(int&t:adj[x])
    {
        if(t!=p)
        {
            int fc1=dp1[t].a+1;
            int fc2=max(dp2[t].a,dp1[t].a+dp1[t].get(dp1[t].a));
            dpex[t]=max(dp2[x].get(fc2),dp1[x].get(fc1)+dp1[x].get(dp1[x].get(fc1),fc1));
            dpe[t]=dp1[x].get(dp1[t].a+1);
            int mx=dp3[x].get(dp1[t].a+1);
            dp3[t].upd(mx+1);
            int mx2=dp3[x].get(mx,dp1[t].a+1);
            int td2=max(dp2[t].a,dp1[t].a+dp1[t].get(dp1[t].a));
            dp4[t].upd(max(dp4[x].get(td2),mx+mx2));
            dfs2(t,x);
        }
    }
    return;
}
const int bufsiz=1<<18;
char buf[bufsiz+10];
int bcnt;
inline int getint()
{
    int a=0;
    while(buf[bcnt]<'0'||buf[bcnt]>'9')
    {
        bcnt++;
        if(bcnt==bufsiz)
        {
            fread(buf,1,bufsiz,stdin);
            bcnt=0;
        }
    }
    while(buf[bcnt]>='0'&&buf[bcnt]<='9')
    {
        a=a*10+buf[bcnt]-'0';
        bcnt++;
        if(bcnt==bufsiz)
        {
            fread(buf,1,bufsiz,stdin);
            bcnt=0;
        }
    }
    return a;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    fread(buf,1,bufsiz,stdin);
    int n,m;
    n=getint(),m=getint();
    vector<pair<pi,int> >ev;
    for(int i=0;i<m;i++)
    {
        int u,v,w;
        u=getint(),v=getint(),w=getint();
        u++,v++;
        if(w==1)
            adj[u].eb(v),adj[v].eb(u);
        else if(w*2<n)
            ev.eb(pi(u,v),w);
    }
    sdfs(1,0);
    int ans=inf;
    {
        int d1=max_element(dep+1,dep+n+1)-dep;
        ddfs(d1,0);
        ans=2*n-1-*max_element(depth+1,depth+n+1);
    }
    dfs2(1,0);
    for(auto&t:ev)
    {
        int u=t.fi.fi;
        int v=t.fi.se;
        int w=t.se;
        int l=lca(u,v);
        int len=dep[u]+dep[v]-dep[l]*2;
        int dmax=0,cmax=0;
        if(v==l)
            swap(u,v);
        if(u==l)
        {
            auto q1=dpth(v,dep[v]-dep[l]-1);
            auto q2=pth(v,dep[v]-dep[l]-1);
            q2.fi++,q2.se++;
            int y=kpa(v,dep[v]-dep[l]-1);
            {
                int fc1=dp1[y].a+1;
                int fc2=max(dp2[y].a,dp1[y].a+dp1[y].get(dp1[y].a));
                int get1=0,get2=0;
                {
                    if(fc1==dp3[l].a)
                        get1=dp3[l].b,get2=dp3[l].c;
                    else
                    {
                        get1=dp3[l].a;
                        if(fc1==dp3[l].b)
                            get2=dp3[l].c;
                        else
                            get2=dp3[l].b;
                    }
                }
                dmax=max({q1,dp4[l].get(fc2),get1+get2});
            }
            {
                int cur=dp3[l].get(dp1[y].a+1);
                cmax=max(q2.se,q2.fi+cur);
            }
        }
        else
        {
            int qu1=dpth(u,dep[u]-dep[l]-1);
            int qv1=dpth(v,dep[v]-dep[l]-1);
            auto qu2=pth(u,dep[u]-dep[l]-1);
            auto qv2=pth(v,dep[v]-dep[l]-1);
            qu2.se++,qv2.se++;
            int yu=kpa(u,dep[u]-dep[l]-1);
            int yv=kpa(v,dep[v]-dep[l]-1);
            {
                int fcu1=dp1[yu].a+1;
                int fcv1=dp1[yv].a+1;
                int fcu2=max(dp2[yu].a,dp1[yu].a+dp1[yu].get(dp1[yu].a));
                int fcv2=max(dp2[yv].a,dp1[yv].a+dp1[yv].get(dp1[yv].a));
                int get1=0,get2=0;
                {
                    int mx=max(fcu1,fcv1),mn=min(fcu1,fcv1);
                    if(mx==dp3[l].a)
                    {
                        if(mn==dp3[l].b)
                            get1=dp3[l].c,get2=dp3[l].d;
                        else if(mn==dp3[l].c)
                            get1=dp3[l].b,get2=dp3[l].d;
                        else
                            get1=dp3[l].b,get2=dp3[l].c;
                    }
                    else if(mn==dp3[l].a)
                        get1=dp3[l].b,get2=dp3[l].c;
                    else
                    {
                        get1=dp3[l].a;
                        if(mx==dp3[l].b)
                        {
                            if(mn==dp3[l].c)
                                get2=dp3[l].d;
                            else
                                get2=dp3[l].c;
                        }
                        else
                            get2=dp3[l].b;
                    }
                }
                dmax=max({qu1,qv1,dp4[l].get(fcu2,fcv2),get1+get2});
            }
            {
                int cur=dp3[l].get(dp1[yu].a+1,dp1[yv].a+1);
                cmax=max({qu2.se+(dep[v]-dep[l]),qv2.se+(dep[u]-dep[l]),qu2.fi+qv2.fi,
                qu2.fi+cur+(dep[v]-dep[l]),qv2.fi+cur+(dep[u]-dep[l])});
            }
        }
        ans=min(ans,n*2-2-dmax-len+w);
        ans=min(ans,n*2-4-cmax+w);
    }
    cout<<ans<<endl;
    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:223:10: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  223 |     fread(buf,1,bufsiz,stdin);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~
Main.cpp: In function 'int getint()':
Main.cpp:203:18: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  203 |             fread(buf,1,bufsiz,stdin);
      |             ~~~~~^~~~~~~~~~~~~~~~~~~~
Main.cpp:213:18: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  213 |             fread(buf,1,bufsiz,stdin);
      |             ~~~~~^~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 1
• Subtask 2: 0 / 2
• Subtask 3: 2 / 2
• Subtask 4: 0 / 6
• Subtask 5: 0 / 2
• Subtask 6: 0 / 3
• Subtask 7: 0 / 5
• Subtask 8: 0 / 4