Submission #223338

#	Time	Username	Problem	Language	Result	Execution time	Memory
223338		cheeheng	Lampice (COCI19_lampice)	C++14	17 / 110	5072 ms	5112 KiB

lampice

#include <bits/stdc++.h>
using namespace std;

char S[50005];

vector<int> AdjList[50005];

const long long MOD = (1LL<<55)-3;
const int MOD2 = 80000001;

long long pow26[50005];

long long dist[50005];
long long dist2[50005];
int dist3[50005];

int main(){
    int N;
    scanf("%d", &N);

    assert(MOD%13 != 0);
    assert(MOD2%13 != 0);

    pow26[0] = 1;
    for(int i = 1; i <= N; i ++){
        pow26[i] = (pow26[i-1]*26)%MOD;
    }

    for(int i = 1; i <= N; i ++){
        scanf(" %c", &S[i]);
    }

    bool subtask2 = true;
    for(int i = 1; i < N; i ++){
        int a, b;
        scanf("%d%d", &a, &b);
        AdjList[a].push_back(b);
        AdjList[b].push_back(a);
        if(a == i && b == i+1 || b == i && a == i+1){
        }else{
            subtask2 = false;
        }
    }

    if(subtask2){
        int ans = 0;
        for(int i = 1; i <= N; i ++){
            int forward1 = 0;
            int backward1 = 0;

            for(int j = i; j <= N; j ++){
                forward1 = (forward1*26+(S[j]-'0'))%MOD2;

                backward1 += pow26[j-i]*(S[j]-'0');
                backward1 %= MOD;

                if(forward1 == backward1){
                    ans = max(ans, j-i+1);
                }
            }
        }
        printf("%d", ans);
        return 0;
    }

    if(N <= 50000){
        int ans = 0;
        for(int i = 1; i <= N; i ++){
            memset(dist, -1, sizeof(dist));
            queue<int> q;
            q.push(i);
            dist[i] = S[i]-'a';
            dist2[i] = S[i]-'a';
            dist3[i] = 0;
            while(!q.empty()){
                int u = q.front(); q.pop();
                for(int v: AdjList[u]){
                    if(dist[v] == -1){
                        dist[v] = (26*dist[u] + (S[v]-'a'))%MOD;
                        dist3[v] = dist3[u]+1;
                        dist2[v] = (pow26[dist3[u]+1]*(S[v]-'a') + dist2[u])%MOD;
                        q.push(v);
                    }
                }
            }

            for(int j = i; j <= N; j ++){
                //printf("%d %d %lld %lld\n", i, j, dist[j], dist2[j]);
                assert(dist[j] != -1);
                if(dist[j] == dist2[j]){
                    ans = max(ans, 1+dist3[j]);
                }
            }
        }

        printf("%d", ans);
        return 0;
    }

    return 0;
}

Compilation message (stderr)

lampice.cpp: In function 'int main()':
lampice.cpp:39:19: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
         if(a == i && b == i+1 || b == i && a == i+1){
            ~~~~~~~^~~~~~~~~~~
lampice.cpp:19:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &N);
     ~~~~~^~~~~~~~~~
lampice.cpp:30:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf(" %c", &S[i]);
         ~~~~~^~~~~~~~~~~~~~
lampice.cpp:36:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &a, &b);
         ~~~~~^~~~~~~~~~~~~~~~

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