Submission #91289

#	Time	Username	Problem	Language	Result	Execution time	Memory
91289		jasony123123	Torrent (COI16_torrent)	C++11	100 / 100	905 ms	24564 KiB

torrent

#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
//using namespace __gnu_pbds;

#define FOR(i,start,end) for(int i=start;i<(int)(end);i++)
#define FORE(i,start,end) for(int i=start;i<=(int)end;i++)
#define RFOR(i,start,end) for(int i = start; i>end; i--)
#define RFORE(i,start,end) for(int i = start; i>=end; i--)
#define all(a) a.begin(), a.end()
#define mt make_tuple
#define mp make_pair
#define v vector
#define sf scanf
#define pf printf
#define dvar(x) cout << #x << " := " << x << "\n"
#define darr(x,n) FOR(i,0,n) cout << #x << "[" << i << "]" << " := " << x[i] << "\n"

typedef long long ll;
typedef long double ld;
typedef pair<int, int > pii;
typedef pair<ll, ll> pll;
//template <class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T> void minn(T &a, T b) { a = min(a, b); }
template<class T> void maxx(T &a, T b) { a = max(a, b); }

void io() {
#ifdef LOCAL_PROJECT 
	freopen("input.in", "r", stdin); freopen("output.out", "w", stdout);
#else 
	/* online submission */

#endif 
	ios_base::sync_with_stdio(false); cin.tie(NULL);
}

const ll MOD = 1000000007LL;
const ll PRIME = 105943LL;
const ll INF = 1e18;
/****************************************************************/

const int MAXN = 300099;
v<int> adj[MAXN];
int N, root1, root2;

bool findpath(int x, int p, int y, v<int> &path) {
	path.push_back(x);
	if (x == y) return 1;
	for (int c : adj[x]) if (c != p)
		if (findpath(c, x, y, path)) return 1;
	path.pop_back();
	return 0;
}

pii delEdge;
int dfsdp(int x, int p) {
	int ans = 0;
	v<int> dpc;
	for (int c : adj[x]) if (c != p && mp(c, x) != delEdge && mp(x, c) != delEdge)
		dpc.push_back(dfsdp(c, x));
	sort(all(dpc)), reverse(all(dpc));
	FOR(i, 0, dpc.size()) maxx(ans, dpc[i] + i + 1);
	return ans;
}

v<int> path;
void change(int i) {
	if (i < path.size() - 1) delEdge = { path[i], path[i + 1] };
	else delEdge = { -1,-1 };
}

int main() {
	io();
	cin >> N >> root1 >> root2;
	FOR(i, 0, N - 1) {
		int x, y;
		cin >> x >> y;
		adj[x].push_back(y);
		adj[y].push_back(x);
	}

	findpath(root1, -1, root2, path);
	assert(path[0] == root1 && path.back() == root2);

	//FOR(i, 0, path.size()) {
	//	if (i < path.size() - 1) delEdge = { path[i], path[i + 1] };
	//	else delEdge = { -1,-1 };
	//	//	cout << i << ": " << dfsdp(root1, -1) << "  " << dfsdp(root2, -1) << "\n";
	//	cout << i << ": " << (dfsdp(root1, -1) < dfsdp(root2, -1)) << "\n";
	//}

	change(0);
	bool sign = dfsdp(root1, -1) < dfsdp(root2, -1);
	int lo = 0, hi = path.size() - 1;
	while (lo < hi) {
		int mid = (lo + hi) / 2;
		change(mid);
		if ((dfsdp(root1, -1) < dfsdp(root2, -1)) == sign)
			lo = mid + 1;
		else
			hi = mid;
	}

	int ans = INT_MAX;
	FORE(i, lo - 5, lo + 5) if (0 <= i && i < path.size()) {
		change(i);
		minn(ans, max(dfsdp(root1, -1), dfsdp(root2, -1)));
	}
	cout << ans << "\n";
	return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'void change(int)':
torrent.cpp:70:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (i < path.size() - 1) delEdge = { path[i], path[i + 1] };
      ~~^~~~~~~~~~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:107:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  FORE(i, lo - 5, lo + 5) if (0 <= i && i < path.size()) {
                                        ~~^~~~~~~~~~~~~

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