Submission #229806

#	Time	Username	Problem	Language	Result	Execution time	Memory
229806		CaroLinda	Islands (IOI08_islands)	C++14	100 / 100	878 ms	131072 KiB

islands

#include <bits/stdc++.h>

#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")

#define mkt make_tuple
#define debug printf
#define all(x) x.begin(),x.end()
#define lp(i,a,b) for(int i = a ; i< b ; i++)
#define ss second
#define ff first
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define mk make_pair

const int MAXN = 1e6+10 ;

using namespace std ;

int N ;
int to[MAXN] ;
ll resp , best_diameter ;
ll W[MAXN] , D[MAXN] ;
ll prof[MAXN];
vector<int> cycle ;
vector< int > adj[MAXN] ;
bool vis[MAXN] ;

void dfs( int x )
{
    vis[x] = true ;

    ll p2 = 0LL ;

    for(int child : adj[x] )
    {
        if(vis[child]) continue ;

        dfs(child) ;

        if( prof[child] + W[child] >= prof[x] )
        {
            p2 = prof[x] ;
            prof[x] = prof[child] + W[child] ;
        }
        else if( prof[child] + W[child] > p2 )
            p2 = prof[child] + W[child] ;

    }

    best_diameter = max( best_diameter, prof[x] + p2 ) ;

}

int main()
{
    scanf("%d", &N ) ;
    for(int i = 1 , u ; i <= N ; i++ )
    {
        scanf("%d%d", &to[i] , &W[i] ) ;
        adj[ to[i] ].pb(i) ;
    }

    for(int j=1 ; j <= N ; j++ )
    {
        if(vis[j]) continue ;

        cycle.clear() ;
        int x = j ;

        while( !vis[x] )
        {
            vis[x] = true ;
            cycle.pb(x) ;
            x = to[x] ;
        }

        reverse( all(cycle) ) ;

        for(int i = cycle.size() - 1 ; cycle[i] != x ; i -- )
        {
            vis[ cycle[i] ] = false ;
            cycle.pop_back() ;
        }

        reverse( all(cycle) ) ;


        best_diameter = 0 ;

        ll sum = 0LL , t = 0LL ;

        for(int i = 0 ; i < cycle.size() ; i++ )
        {
            dfs( cycle[i] ) ;
            sum += W[ cycle[i] ] ;
            if( i ) D[ cycle[i] ] = D[ cycle[i-1] ] + W[ cycle[i-1] ] ;
        }

        for(int i = 0 ; i < cycle.size() ; i++ )
        {
            if( i ) best_diameter = max( best_diameter , t + D[ cycle[i] ] + prof[ cycle[i] ] ) ;
            t = max(t , -D[ cycle[i] ] + prof[ cycle[i] ] ) ;
        }

        t = 0LL ;
        for(int i = 0 ; i < cycle.size() ; i++ )
        {
            if(i) best_diameter = max( best_diameter , sum - D[ cycle[i] ] + prof[ cycle[i] ] + t ) ;
            t = max( t , D[ cycle[i] ] + prof[ cycle[i] ] ) ;
        }

        resp += best_diameter ;
    }

    printf("%lld\n" , resp ) ;

}

Compilation message (stderr)

islands.cpp:4:0: warning: ignoring #pragma GCC optimization [-Wunknown-pragmas]
 #pragma GCC optimization ("O3")
 
islands.cpp:5:0: warning: ignoring #pragma GCC optimization [-Wunknown-pragmas]
 #pragma GCC optimization ("unroll-loops")
 
islands.cpp: In function 'int main()':
islands.cpp:62:38: warning: format '%d' expects argument of type 'int*', but argument 3 has type 'long long int*' [-Wformat=]
         scanf("%d%d", &to[i] , &W[i] ) ;
                                ~~~~~ ^
islands.cpp:60:21: warning: unused variable 'u' [-Wunused-variable]
     for(int i = 1 , u ; i <= N ; i++ )
                     ^
islands.cpp:95:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0 ; i < cycle.size() ; i++ )
                         ~~^~~~~~~~~~~~~~
islands.cpp:102:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0 ; i < cycle.size() ; i++ )
                         ~~^~~~~~~~~~~~~~
islands.cpp:109:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0 ; i < cycle.size() ; i++ )
                         ~~^~~~~~~~~~~~~~
islands.cpp:59:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &N ) ;
     ~~~~~^~~~~~~~~~~
islands.cpp:62:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &to[i] , &W[i] ) ;
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 10 / 10