Submission #817655

#	Time	Username	Problem	Language	Result	Execution time	Memory
817655		LucaIlie	Mergers (JOI19_mergers)	C++17	100 / 100	1483 ms	155884 KiB

mergers

#include <bits/stdc++.h>
 
using namespace std;
 
const int MAX_N = 5e5;
int state[MAX_N + 1], depth[MAX_N + 1], parent[MAX_N + 1], preord[MAX_N + 1];
vector<int> edges[MAX_N + 1], cities[MAX_N + 1];
set<int> stateEdges[MAX_N + 1];
 
struct DSU {
    int comp;
    int p[MAX_N + 1];
 
    void init( int k ) {
        for ( int u = 1; u <= k; u++ )
            p[u] = u;
        comp = k;
    }
 
    int find( int u ) {
        if ( p[u] == u )
            return u;
        p[u] = find( p[u] );
        return p[u];
    }
 
    void merge( int u, int v ) {
        u = find( u );
        v = find( v );
        if ( u == v )
            return;
 
        comp--;
        p[u] = v;
    }
} dsu;
 
int pre = 0;
void dfs( int u, int p ) {
    parent[u] = p;
    depth[u] = depth[p] + 1;
    preord[u] = pre++;
    for ( int v: edges[u] ) {
        if ( v == p )
            continue;
        dfs( v, u );
    }
}
 
int main() {
    int n, k;
 
    cin >> n >> k;
    for ( int i = 0; i < n - 1; i++ ) {
        int u, v;
        cin >> u >> v;
        edges[u].push_back( v );
        edges[v].push_back( u );
    }
    for ( int u = 1; u <= n; u++ ) {
        cin >> state[u];
        cities[state[u]].push_back( u );
    }
 
    dfs( 1, 0 );
 
    dsu.init( k );
    for ( int s = 1; s <= k; s++ ) {
        sort( cities[s].begin(), cities[s].end(), []( int u, int v ) {
            return preord[u] < preord[v];
        } );
        for ( int i = 0; i < cities[s].size() - 1; i++ ) {
            int u = cities[s][i], v = cities[s][i + 1];
            while ( depth[u] > depth[v] ) {
                dsu.merge( state[u], state[parent[u]] );
                u = parent[u];
            }
            while ( depth[v] > depth[u] ) {
                dsu.merge( state[v], state[parent[v]] );
                v = parent[v];
            }
            while ( u != v ) {
                dsu.merge( state[u], state[parent[u]] );
                u = parent[u];
                dsu.merge( state[v], state[parent[v]] );
                v = parent[v];
            }
        }
    }
 
    for ( int u = 1; u <= n; u++ )
        state[u] = dsu.find( state[u] );
 
    for ( int u = 1; u <= n; u++ ) {
        for ( int v: edges[u] ) {
            if ( state[u] == state[v] )
                continue;
            stateEdges[state[u]].insert( state[v] );
            stateEdges[state[v]].insert( state[u] );
        }
    }
 
    int leafs = 0;
    for ( int s = 1; s <= k; s++ ) {
        if ( stateEdges[s].size() == 1 )
            leafs++;
    }
 
    cout << (leafs + 1) / 2;
 
    return 0;
}

Compilation message (stderr)

mergers.cpp: In function 'int main()':
mergers.cpp:72:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   72 |         for ( int i = 0; i < cities[s].size() - 1; i++ ) {
      |                          ~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 24 / 24
• Subtask 3: 14 / 14
• Subtask 4: 22 / 22
• Subtask 5: 30 / 30