Submission #1264507

#	Time	Username	Problem	Language	Result	Execution time	Memory
1264507		cattuong	Lampice (COCI19_lampice)	C++20	0 / 110	3 ms	3912 KiB

lampice

/* I LOVE CATTUONG */
//
#include <bits/stdc++.h>
#define CatTuong ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
using namespace std;
#define int long long
const int N=5e4+5;
const int base=311;
const int MOD=1e9+7;
int sz[N],n,H,h[N],preH[N],suffH[N],powB[N],mx_h,ans;
char a[N];
bool is_cen[N];
map<int,bool>mp[N];
vector<int>g[N];
//abc cba
//palin H abc*powb[H-sz(len)]-cba
int add(int x,int y){return (x+y)%MOD;}
int mul(int x,int y){return (x*y)%MOD;}
int sub(int x,int y){return ((x-y)+MOD)%MOD;}
void DFS(int u,int p){
    sz[u]=1;
    for(auto v:g[u]){
        if(v!=p && !is_cen[v]){
            DFS(v,u);
            sz[u]+=sz[v];
        }
    }
}
int find_cen(int u,int p,int tree_sz){
    for(auto v:g[u]){
        if(v!=p && !is_cen[v] && sz[v]>tree_sz/2){
            return find_cen(v,u,tree_sz);
        }
    }
    return u;
}
int get(int u,int p){
    h[u]=h[p]+1;
    if(h[u]>H)
        return 0;
    mx_h=max(mx_h,h[u]);
    preH[h[u]]=add(mul(preH[h[u]-1],base),a[u]);
    suffH[h[u]]=add(suffH[h[u]-1],mul(a[u],powB[h[u]-1]));
    int tmp=sub(mul(suffH[h[u]],powB[H-h[u]]),preH[h[u]]);
    if(preH[h[u]]==suffH[h[u]] && h[u]==H)
        return 1;
    if(mp[H-h[u]].find(tmp)!=mp[H-h[u]].end())
        return 1;
    for(auto v:g[u]){
        if(v!=p && !is_cen[v]){
            if(get(v,u))
                return 1;
        }
    }
    return 0;
}
void update(int u,int p){
    h[u]=h[p]+1;
    if(h[u]>H)
        return;
    mx_h=max(mx_h,h[u]);
    preH[h[u]]=add(mul(preH[h[u]-1],base),a[u]);
    suffH[h[u]]=add(suffH[h[u]-1],mul(a[u],powB[h[u]-1]));
    int tmp=sub(mul(suffH[h[u]],powB[H-h[u]]),preH[h[u]]);
    mp[h[u]][tmp]=1;
    for(auto v:g[u]){
        if(v!=p && !is_cen[v])
            update(v,u);
    }
}
bool build_cen(int u){
    DFS(u,-1);
    int cen=find_cen(u,-1,sz[u]);
    is_cen[cen]=true;
    for(auto v:g[cen]){
        if(v!=cen && !is_cen[v]){
            h[cen]=1;
            suffH[1]=preH[1]=a[cen];
            if(get(v,cen))
                return 1;
            h[cen]=preH[0]=suffH[0]=0;
            update(v,cen);
        }
    }
    for(int i=0;i<=mx_h;++i){
        mp[i].clear();
    }
    mx_h=0;
    for(auto v:g[cen]){
        if(!is_cen[v]){
            if(build_cen(v))
                return 1;
        }
    }
    return 0;
}
bool check(int x){
    for(int i=1;i<=n;++i){
        mp[i].clear();
        is_cen[i]=false;
    }
    H=x;
    return build_cen(1);
}
signed main(){
    #define Tuong "LAMPICE"
    freopen(Tuong".inp","r",stdin);
    freopen(Tuong".out","w",stdout);
    CatTuong
    cin>>n;
    for(int i=1;i<=n;++i){
        cin>>a[i];
    }
    for(int i=1;i<n;++i){
        int u,v;cin>>u>>v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    powB[0]=1;
    for(int i=1;i<=n;++i)
        powB[i]=mul(powB[i-1],base);
    int lo=0,hi=n;
    while(hi>=lo){
        int mid=(hi+lo)>>1;
        if(check(2*mid) && 2*mid<=n){
            ans=2*mid;
            lo=mid+1;
        }
        else
            hi=mid-1;
    }
    lo=0,hi=n;
    while(hi>=lo){
        int mid=(hi+lo)>>1;
        if(check(2*mid+1) && 2*mid+1<=n){
            ans=max(ans,2*mid+1);
            lo=mid+1;
        }
        else
            hi=mid-1;
    }
    cout<<ans;
    return 0;
}

Compilation message (stderr)

lampice.cpp: In function 'int main()':
lampice.cpp:107:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  107 |     freopen(Tuong".inp","r",stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
lampice.cpp:108:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  108 |     freopen(Tuong".out","w",stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 17
• Subtask 2: 0 / 25
• Subtask 3: 0 / 31
• Subtask 4: 0 / 37