Submission #226454

#	Time	Username	Problem	Language	Result	Execution time	Memory
226454		rqi	Network (BOI15_net)	C++14	100 / 100	655 ms	91000 KiB

net

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef double db; 
typedef string str; 

typedef pair<int,int> pi;
typedef pair<ll,ll> pl; 
typedef pair<db,db> pd; 

typedef vector<int> vi; 
typedef vector<ll> vl; 
typedef vector<db> vd; 
typedef vector<str> vs; 
typedef vector<pi> vpi;
typedef vector<pl> vpl; 
typedef vector<pd> vpd; 

#define mp make_pair 
#define f first
#define s second
#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend() 
#define rsz resize
#define ins insert 
#define ft front() 
#define bk back()
#define pf push_front 
#define pb push_back
#define eb emplace_back 
#define lb lower_bound 
#define ub upper_bound 

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5; 
const ll INF = 1e18; 
const ld PI = acos((ld)-1);
const int xd[4] = {1,0,-1,0}, yd[4] = {0,1,0,-1}; 

template<class T> bool ckmin(T& a, const T& b) { 
    return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { 
    return a < b ? a = b, 1 : 0; } 
int pct(int x) { return __builtin_popcount(x); } 
int bit(int x) { return 31-__builtin_clz(x); } // floor(log2(x)) 
int cdiv(int a, int b) { return a/b+!(a<0||a%b == 0); } // division of a by b rounded up, assumes b > 0 

// INPUT
template<class A> void re(complex<A>& c);
template<class A, class B> void re(pair<A,B>& p);
template<class A> void re(vector<A>& v);
template<class A, size_t SZ> void re(array<A,SZ>& a);

template<class T> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
template<class H, class... T> void re(H& h, T&... t) { re(h); re(t...); }

template<class A> void re(complex<A>& c) { A a,b; re(a,b); c = {a,b}; }
template<class A, class B> void re(pair<A,B>& p) { re(p.f,p.s); }
template<class A> void re(vector<A>& x) { trav(a,x) re(a); }
template<class A, size_t SZ> void re(array<A,SZ>& x) { trav(a,x) re(a); }

// TO_STRING
#define ts to_string
template<class A, class B> str ts(pair<A,B> p);
template<class A> str ts(complex<A> c) { return ts(mp(c.real(),c.imag())); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(char c) { str s = ""; s += c; return s; }
str ts(str s) { return s; }
str ts(const char* s) { return (str)s; }
str ts(vector<bool> v) { 
    bool fst = 1; str res = "{";
    F0R(i,sz(v)) {
        if (!fst) res += ", ";
        fst = 0; res += ts(v[i]);
    }
    res += "}"; return res;
}
template<size_t SZ> str ts(bitset<SZ> b) {
    str res = ""; F0R(i,SZ) res += char('0'+b[i]);
    return res; }
template<class T> str ts(T v) {
    bool fst = 1; str res = "{";
    for (const auto& x: v) {
        if (!fst) res += ", ";
        fst = 0; res += ts(x);
    }
    res += "}"; return res;
}
template<class A, class B> str ts(pair<A,B> p) {
    return "("+ts(p.f)+", "+ts(p.s)+")"; }

// OUTPUT
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) { 
    pr(h); pr(t...); }
void ps() { pr("\n"); } // print w/ spaces
template<class H, class... T> void ps(const H& h, const T&... t) { 
    pr(h); if (sizeof...(t)) pr(" "); ps(t...); }

// DEBUG
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << to_string(h); if (sizeof...(t)) cerr << ", ";
    DBG(t...); }
#ifdef LOCAL // compile with -DLOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 42
#endif

// FILE I/O
void setIn(string s) { freopen(s.c_str(),"r",stdin); }
void setOut(string s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { ios_base::sync_with_stdio(0); cin.tie(0); }
void setIO(string s = "") {
    unsyncIO();
    // cin.exceptions(cin.failbit); 
    // throws exception when do smth illegal
    // ex. try to read letter into int
    if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
}

mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count()); 

const int mx = 500005;
vi adj[mx];
int sub[mx];
int to;
int cent;
int tot;

void genSub(int node, int prv = -1){
    if(sz(adj[node]) == 1){
        sub[node] = 1;
        tot++;
        return;
    }
    for(auto u: adj[node]){
        if(u == prv) continue;
        genSub(u, node);
        sub[node]+=sub[u];
    }
}

void genCent(int node, int prv = -1){
    for(auto u: adj[node]){
        if(u == prv) continue;
        if(sub[u]*2 > tot){
            genCent(u, node);
            return;
        }
    }
    cent = node;
}

vi leaves[mx];

void labelLeaves(int node, int prv, int label){
    if(sz(adj[node]) == 1) leaves[label].pb(node);
    for(auto u: adj[node]){
        if(u == prv) continue;
        labelLeaves(u, node, label);
    }
}

vi szs[mx];

int main() {
    setIO();
    int n;
    cin >> n;
    for(int i = 0; i < n-1; i++){
        int a, b;
        cin >> a >> b;
        adj[a].pb(b);
        adj[b].pb(a);
    }
    for(int i = 1; i <= n; i++){
        if(sz(adj[i]) > 1){
            to = i;
        }
    }
    genSub(to);
    genCent(to);
    for(int i = 0; i < sz(adj[cent]); i++){
        labelLeaves(adj[cent][i], cent, i);
    }
    int m = sz(adj[cent]);

    vpi ans;
    int curmx = 0;
    for(int i = 0; i < m; i++){
        szs[sz(leaves[i])].pb(i);
        ckmax(curmx, sz(leaves[i]));
    }
    int mx1 = curmx;
    int mx2 = curmx;
    /*dbg(cent);
    for(int i = 0; i < m; i++){
        dbg(i, szs[i]);
    }*/
    for(int i = 0; i < (tot+1)/2; i++){
        while(mx1 > 0 && sz(szs[mx1]) == 0){
            mx1--;
        }
        while(mx2 > 0 && ((mx2 > mx1) || (sz(szs[mx2]) == 0) || ((mx2 == mx1) && (sz(szs[mx1]) == 1)))){
            mx2--;
        }
        //dbg(ans, mx1, mx2);
        if(mx2 != 0){
            int a = szs[mx1].bk;
            szs[mx1].pop_back();
            int b = szs[mx2].bk;
            szs[mx2].pop_back();
            szs[mx1-1].pb(a);
            szs[mx2-1].pb(b);
            ans.pb(mp(leaves[a].bk, leaves[b].bk));
            leaves[a].pop_back();
            leaves[b].pop_back();
        }
        else if(mx1 > 0){
            int a = szs[mx1].bk;
            int node1 = leaves[a].bk;
            ans.pb(mp(node1, cent));
        }
    }
    ps(sz(ans));
    for(auto u: ans){
        cout << u.f << " " << u.s << "\n";
    }

    // you should actually read the stuff at the bottom
}

/* stuff you should look for
    * int overflow, array bounds
    * special cases (n=1?)
    * do smth instead of nothing and stay organized
    * WRITE STUFF DOWN
*/

Compilation message (stderr)

net.cpp: In function 'void setIn(std::__cxx11::string)':
net.cpp:123:31: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setIn(string s) { freopen(s.c_str(),"r",stdin); }
                        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
net.cpp: In function 'void setOut(std::__cxx11::string)':
net.cpp:124:32: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setOut(string s) { freopen(s.c_str(),"w",stdout); }
                         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

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