Submission #531521

#	Time	Username	Problem	Language	Result	Execution time	Memory
531521		zlxFTH	Torrent (COI16_torrent)	C++11	0 / 100	2071 ms	7244 KiB

torrent

#include<bits/stdc++.h>
#define LL long long
#define Rep(i,x,y) for(int i = (x), stOxrj = (y); i <= stOxrj; ++i)
#define Irep(i,x,y) for(int i = (x), stOxrj = (y); i >= stOxrj; --i)
#define il inline
#define let const auto
#define ci const int&
#define VEC vector<int>
#define pb emplace_back
#define MP make_pair
#define PA pair<int, int>
#define fi first
#define se second
#define IT iterator
using namespace std;
il int read(){
	int res = 0, flag = 1; char c = getchar();
	while( c < '0' || c > '9' ){ if( c == '-' ) flag = -1; c = getchar(); }
	while( c >= '0' && c <= '9' ) res = res * 10 + c - '0', c = getchar();
	return res * flag;
}
const int N = 3e5 + 20;
VEC e[N];
int ba, bb, n, s, t;
bool same(ci u, ci v){
	return u + v == ba + bb && abs(u - v) == abs(ba - bb);
}
int fa[N], f[N];
int nb[N];
void dfs(int u, int fat){
	fa[u] = fat;
	for(int v : e[u]) if(v != fat && !same(u, v)) dfs(v, u);
	int res = 0, cnt = 0;
	for(int v : e[u]) if(v != fat && !same(u, v)) nb[++cnt] = f[v];
	sort(nb + 1, nb + cnt + 1, [&](ci A, ci B){ return A > B; });
	Rep(i, 1, cnt) res = max(res, i + nb[i]);
	f[u] = res;	
}
int link[N], ln;
PA Solve(int x){
	ba = link[x], bb = link[x + 1];
	dfs(s, 0), dfs(t, 0);
	return MP(f[s], f[t]);
}
signed main(){
	freopen("torrent.in", "r", stdin);
	freopen("torrent.out", "w", stdout);
	n = read(), s = read(), t = read();
	Rep(i, 2, n){
		int u = read(), v = read();
		e[u].pb(v), e[v].pb(u);
	}
	dfs(t, 0);
	int ss = s;
	link[++ln] = s;
	while(ss != t) link[++ln] = ss = fa[ss];

	PA cur;
	int l = 1, r = ln - 1;
	while(l < r){
		int mid = l + r >> 1;
		cur = Solve(mid);
		if(cur.fi > cur.se) l = mid + 1;
		else r = mid;
	}
	cur = Solve(l);
	int ans = max(cur.fi, cur.se);
	if(l != 1){
		cur = Solve(l - 1);
		ans = min(ans, max(cur.fi, cur.se));
	}	
	cout<<ans<<'\n';
	return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int main()':
torrent.cpp:61:15: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   61 |   int mid = l + r >> 1;
      |             ~~^~~
torrent.cpp:46:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   46 |  freopen("torrent.in", "r", stdin);
      |  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:47:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   47 |  freopen("torrent.out", "w", stdout);
      |  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

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