Submission #399345

#	Time	Username	Problem	Language	Result	Execution time	Memory
399345		cpp219	Network (BOI15_net)	C++14	0 / 100	8 ms	12016 KiB

net

#pragma GCC optimization "O2"
#pragma GCC optimization "unroll-loop"
#pragma GCC target ("avx2")

#include<bits/stdc++.h>
#define ll int
#define ld long double
#define fs first
#define sc second
using namespace std;
typedef pair<ll,ll> LL;
const ll N = 5e5 + 9;
const ll inf = 1e9 + 7;
const ll Log2 = 21;
vector<ll> g[N];
deque<ll> leaf;
vector<LL> ans;
ll n,x,y,root,pos[N],d[N],par[N][Log2];
ll now;
void DFS(ll u,ll p){
    pos[u] = now; now++;
    for (ll i = 1;i < Log2;i++) if ((1 << u) <= d[u])
        par[u][i] = par[par[u][i - 1]][i - 1];
    for (auto i : g[u]){
        if (i != p){
            d[i] = d[u] + 1; par[i][0] = u;
            DFS(i,u);
        }
    }
}

bool lf(ll x,ll y){
    return pos[x] < pos[y];
}

ll LCA(ll u,ll v){
    if (d[u] > d[v]) swap(u,v);
    for (ll i = Log2 - 1;i >= 0;i--) if ((1 << i) <= d[v] && d[par[v][i]] >= d[u])
        v = par[v][i];
    if (u == v) return u;
    for (ll i = Log2 - 1;i >= 0;i--) if (par[u][i] != par[v][i])
        v = par[v][i],u = par[u][i];
    return par[v][0];
}

ll nearest(ll target){
    ll scr = leaf.front();
    ll l = 0,h = leaf.size() - 1,m;
    while(l <= h){
        m = (l + h)/2;
        //cout<<scr<<" "<<leaf[m]<<" "<<LCA(scr,leaf[m])<<"\n"; //exit(0);
        if (LCA(scr,leaf[m]) == target) h = m - 1;
        else l = m + 1;
    }
    //exit(0);
    //cout<<leaf[l]<<" "<<LCA(scr,leaf[l]); exit(0);
    return l;
}

void out(){
    for (auto i : leaf) cout<<i<<" "; exit(0);
}

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    #define task "tst"
    if (fopen(task".inp","r")){
        freopen(task".inp","r",stdin);
        //freopen(task".out","w",stdout);
    }
    cin>>n;
    for (ll i = 1;i < n;i++){
        cin>>x>>y;
        g[x].push_back(y); g[y].push_back(x);
    }
    for (ll i = 1;i <= n;i++){
        if (g[i].size() > 1) root = i;
        else leaf.push_back(i);
    }
    DFS(root,0); sort(leaf.begin(),leaf.end(),lf);
    while(!leaf.empty()){
        ll sz = leaf.size();
        if (sz == 1) break;
        ll lca = LCA(leaf.front(),leaf.back());
        ll nxt = nearest(lca);
        if (nxt <= sz/2){
            for (ll i = 0;i < nxt;i++) ans.push_back({leaf[i],leaf[nxt + i]});
            for (ll i = 0;i < 2*nxt;i++) leaf.pop_front();
        }
        else{
            for (ll i = sz - 1;i >= nxt;i--) ans.push_back({leaf[i],leaf[nxt - sz + i]});
            for (ll i = 0;i < 2*(sz - nxt);i++) leaf.pop_back();
        }
        //out();
    }
    if (!leaf.empty()) ans.push_back({leaf.back(),root});
    cout<<ans.size()<<"\n";
    for (auto i : ans) cout<<i.fs<<" "<<i.sc<<"\n";
}

Compilation message (stderr)

net.cpp:1: warning: ignoring #pragma GCC optimization [-Wunknown-pragmas]
    1 | #pragma GCC optimization "O2"
      | 
net.cpp:2: warning: ignoring #pragma GCC optimization [-Wunknown-pragmas]
    2 | #pragma GCC optimization "unroll-loop"
      | 
net.cpp: In function 'void out()':
net.cpp:61:5: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
   61 |     for (auto i : leaf) cout<<i<<" "; exit(0);
      |     ^~~
net.cpp:61:39: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   61 |     for (auto i : leaf) cout<<i<<" "; exit(0);
      |                                       ^~~~
net.cpp: In function 'int main()':
net.cpp:68:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   68 |         freopen(task".inp","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37