Submission #846660

#	Time	Username	Problem	Language	Result	Execution time	Memory
846660		vjudge1	Torrent (COI16_torrent)	C++14	31 / 100	53 ms	28244 KiB

torrent

#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
using db = double;
using str = string;  // yay python!

using pi = pair<int, int>;
using pl = pair<ll, ll>;
using pd = pair<db, db>;

using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vpi = vector<pi>;
using vpl = vector<pl>;
using vpd = vector<pd>;

#define tcT template <class T
#define tcTU tcT, class U
// ^ lol this makes everything look weird but I'll try it
tcT > using V = vector<T>;
tcT, size_t SZ > using AR = array<T, SZ>;
tcT > using PR = pair<T, T>;

// pairs
#define mp make_pair
#define f first
#define s second

// vectors
// oops size(x), rbegin(x), rend(x) need C++17
#define sz(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) x.rbegin(), x.rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front

#define lb lower_bound
#define ub upper_bound
tcT > int lwb(V<T> &a, const T &b) { return int(lb(all(a), b) - bg(a)); }

// loops
#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;  // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1, 0, -1, 0},
          dy[4] = {0, 1, 0, -1};  // for every grid problem!!
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
template <class T> using pqg = priority_queue<T, vector<T>, greater<T>>;

// bitwise ops
// also see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
constexpr int pct(int x) { return __builtin_popcount(x); }  // # of bits set
constexpr int bits(int x) {  // assert(x >= 0); // make C++11 compatible until
	                         // USACO updates ...
	return x == 0 ? 0 : 31 - __builtin_clz(x);
}  // floor(log2(x))
constexpr int p2(int x) { return 1 << x; }
constexpr int msk2(int x) { return p2(x) - 1; }

ll cdiv(ll a, ll b) {
	return a / b + ((a ^ b) > 0 && a % b);
}  // divide a by b rounded up
ll fdiv(ll a, ll b) {
	return a / b - ((a ^ b) < 0 && a % b);
}  // divide a by b rounded down

tcT > bool ckmin(T &a, const T &b) {
	return b < a ? a = b, 1 : 0;
}  // set a = min(a,b)
tcT > bool ckmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }

tcTU > T fstTrue(T lo, T hi, U f) {
	hi++;
	assert(lo <= hi);  // assuming f is increasing
	while (lo < hi) {  // find first index such that f is true
		T mid = lo + (hi - lo) / 2;
		f(mid) ? hi = mid : lo = mid + 1;
	}
	return lo;
}
tcTU > T lstTrue(T lo, T hi, U f) {
	lo--;
	assert(lo <= hi);  // assuming f is decreasing
	while (lo < hi) {  // find first index such that f is true
		T mid = lo + (hi - lo + 1) / 2;
		f(mid) ? lo = mid : hi = mid - 1;
	}
	return lo;
}
tcT > void remDup(vector<T> &v) {  // sort and remove duplicates
	sort(all(v));
	v.erase(unique(all(v)), end(v));
}
tcTU > void erase(T &t, const U &u) {  // don't erase
	auto it = t.find(u);
	assert(it != end(t));
	t.erase(it);
}  // element that doesn't exist from (multi)set

// INPUT
#define tcTUU tcT, class... U
tcT > void re(complex<T> &c);
tcTU > void re(pair<T, U> &p);
tcT > void re(V<T> &v);
tcT, size_t SZ > void re(AR<T, SZ> &a);

tcT > 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);
}
tcTUU > void re(T &t, U &...u) {
	re(t);
	re(u...);
}

tcT > void re(complex<T> &c) {
	T a, b;
	re(a, b);
	c = {a, b};
}
tcTU > void re(pair<T, U> &p) { re(p.f, p.s); }
tcT > void re(V<T> &x) { trav(a, x) re(a); }
tcT, size_t SZ > void re(AR<T, SZ> &x) { trav(a, x) re(a); }
tcT > void rv(int n, V<T> &x) {
	x.rsz(n);
	re(x);
}

// TO_STRING
#define ts to_string
str ts(char c) { return str(1, c); }
str ts(const char *s) { return (str)s; }
str ts(str s) { return s; }
str ts(bool b) {
#ifdef LOCAL
	return b ? "true" : "false";
#else
	return ts((int)b);
#endif
}
tcT > str ts(complex<T> c) {
	stringstream ss;
	ss << c;
	return ss.str();
}
str ts(V<bool> v) {
	str res = "{";
	F0R(i, sz(v)) res += char('0' + 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;
}
tcTU > str ts(pair<T, U> p);
tcT > str ts(T v) {  // containers with begin(), end()
#ifdef LOCAL
	bool fst = 1;
	str res = "{";
	for (const auto &x : v) {
		if (!fst) res += ", ";
		fst = 0;
		res += ts(x);
	}
	res += "}";
	return res;
#else
	bool fst = 1;
	str res = "";
	for (const auto &x : v) {
		if (!fst) res += " ";
		fst = 0;
		res += ts(x);
	}
	return res;

#endif
}
tcTU > str ts(pair<T, U> p) {
#ifdef LOCAL
	return "(" + ts(p.f) + ", " + ts(p.s) + ")";
#else
	return ts(p.f) + " " + ts(p.s);
#endif
}

// OUTPUT
tcT > void pr(T x) { cout << ts(x); }
tcTUU > void pr(const T &t, const U &...u) {
	pr(t);
	pr(u...);
}
void ps() { pr("\n"); }  // print w/ spaces
tcTUU > void ps(const T &t, const U &...u) {
	pr(t);
	if (sizeof...(u)) pr(" ");
	ps(u...);
}

// DEBUG
void DBG() { cerr << "]" << endl; }
tcTUU > void DBG(const T &t, const U &...u) {
	cerr << ts(t);
	if (sizeof...(u)) cerr << ", ";
	DBG(u...);
}
#ifdef LOCAL  // compile with -DLOCAL, chk -> fake assert
#define dbg(...)                                                               \
	cerr << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [",         \
	    DBG(__VA_ARGS__)
#define chk(...)                                                               \
	if (!(__VA_ARGS__))                                                        \
		cerr << "Line(" << __LINE__ << ") -> function(" << __FUNCTION__        \
		     << ") -> CHK FAILED: (" << #__VA_ARGS__ << ")"                    \
		     << "\n",                                                          \
		    exit(0);
#else
#define dbg(...) 0
#define chk(...) 0
#endif

void setPrec() { cout << fixed << setprecision(15); }
void unsyncIO() { cin.tie(0)->sync_with_stdio(0); }
// FILE I/O
void setIn(str s) { freopen(s.c_str(), "r", stdin); }
void setOut(str s) { freopen(s.c_str(), "w", stdout); }
void setIO(str s = "") {
	unsyncIO();
	setPrec();
	// 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
}

int N, A, B, par[MX];
bool inPath[MX];
vi adj[MX];

void dfs(int x) {
	trav(t, adj[x]) if (par[t] == 0) {
		par[t] = x;
		dfs(t);
	}
}

int need(int x, int y) {
	vi tri;
	trav(t, adj[x]) if (!inPath[t] && t != y) tri.pb(need(t, x));
	sort(rall(tri));
	int ans = 0;
	F0R(i, sz(tri)) ckmax(ans, i + 1 + tri[i]);
	return ans;
}

int get_max(
    int res, vi ans,
    vi path) {  // find max length prefix of path so that answer is <= res
	int cur = 0;
	F0R(i, sz(ans)) {
		if (ans[i] + cur > res) return i;
		if (ans[i] + cur < res) {
			cur++;
			continue;
		}  // just send to next node on path
		int x = path[i];
		vi tri;
		trav(t, adj[x]) if (!inPath[t]) tri.pb(need(t, x));
		sort(rall(tri));
		F0R(z, sz(tri)) tri[z] += 1 + z;
		R0F(z, sz(tri) - 1) ckmax(tri[z], tri[z + 1]);
		trav(t, tri) cur += t == tri[0];
		cur++;
	}
	return sz(ans);
}

int main() {
	setIO();
	re(N, A, B);
	F0R(i, N - 1) {
		int x, y;
		re(x, y);
		adj[x].pb(y), adj[y].pb(x);
	}
	par[A] = -1;
	dfs(A);
	vi path = {B};
	while (path.bk != A) path.pb(par[path.bk]);
	trav(t, path) inPath[t] = 1;
	vi ans;
	trav(t, path) ans.pb(need(t, -1));
	int res = 0;
	F0R(i, sz(ans)) ckmax(res, ans[i] + min(sz(ans) - 1 - i, i) + 1);
	// greedy strategy: first the computers send to each other and then to the
	// rest of the tree
	int max_pref = get_max(res - 1, ans, path);
	reverse(all(path)), reverse(all(ans));
	int max_pref_2 = get_max(res - 1, ans, path);
	// check if you can get one better than greedy strategy
	if (max_pref + max_pref_2 >= sz(path)) ps(res - 1);
	else ps(res);
}

Compilation message (stderr)

torrent.cpp: In function 'void setIn(str)':
torrent.cpp:253:28: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  253 | void setIn(str s) { freopen(s.c_str(), "r", stdin); }
      |                     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp: In function 'void setOut(str)':
torrent.cpp:254:29: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  254 | void setOut(str s) { freopen(s.c_str(), "w", stdout); }
      |                      ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 31 / 31
• Subtask 2: 0 / 69