Submission #640348

#	Time	Username	Problem	Language	Result	Execution time	Memory
640348		PoonYaPat	Roadside Advertisements (NOI17_roadsideadverts)	C++14	100 / 100	78 ms	11028 KiB

roadsideadverts

#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;

int n,m,a[6];
vector<pii> adj[50001];
int level[50001],p[50001][17],dis[50001];

void dfs(int x, int par) {
    level[x]=level[par]+1;
    p[x][0]=par;
    for (int i=1; i<=16; ++i) {
        p[x][i]=p[p[x][i-1]][i-1];
    }

    for (auto s : adj[x]) {
        if (s.first==par) continue;
        dis[s.first]=dis[x]+s.second;
        dfs(s.first,x);
    }
}

int lca(int x, int y) {
    if (level[x]<level[y]) swap(x,y);

    int dif=level[x]-level[y];
    for (int i=0; i<=16; ++i) {
        if (dif&(1<<i)) x=p[x][i];
    }
    if (x==y) return x;

    for (int i=16; i>=0; --i) {
        if (p[x][i]!=p[y][i]) {
            x=p[x][i];
            y=p[y][i];
        }
    }
    return p[x][0];
}

int dist(int x, int y) {
    return dis[x]+dis[y]-2*dis[lca(x,y)];
}

void solve() {
    for (int i=1; i<=5; ++i) cin>>a[i];
    int top_node, min_level=INT_MAX;

    for (int i=2; i<=5; ++i) {
        int node=lca(a[1],a[i]);
        if (level[node]<min_level) {
            min_level=level[node];
            top_node=node;
        }
    }

    vector<pii> v; //(level,node)
    for (int i=1; i<=5; ++i) v.push_back(pii(level[a[i]],a[i]));
    sort(v.begin(),v.end());

    int ans=0;
    for (int i=0; i<5; ++i) {
        int node=v[i].second;
        int mmin=dist(top_node,node);
        for (int j=0; j<i; ++j) mmin=min(mmin,dis[node]-dis[lca(node,v[j].second)]);
        ans+=mmin;
    }
    cout<<ans<<"\n";
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin>>n;
    for (int i=0; i<n-1; ++i) {
        int x,y,w;
        cin>>x>>y>>w;
        adj[x].push_back(pii(y,w));
        adj[y].push_back(pii(x,w));
    }
    dfs(0,0);
    cin>>m;
    while (m--) solve();
}

Compilation message (stderr)

roadsideadverts.cpp: In function 'void solve()':
roadsideadverts.cpp:42:35: warning: 'top_node' may be used uninitialized in this function [-Wmaybe-uninitialized]
   42 |     return dis[x]+dis[y]-2*dis[lca(x,y)];
      |                                ~~~^~~~~
roadsideadverts.cpp:47:9: note: 'top_node' was declared here
   47 |     int top_node, min_level=INT_MAX;
      |         ^~~~~~~~

• Subtask 1: 7 / 7
• Subtask 2: 23 / 23
• Subtask 3: 40 / 40
• Subtask 4: 30 / 30