Submission #541905

#	Time	Username	Problem	Language	Result	Execution time	Memory
541905		Asymmetry	Mousetrap (CEOI17_mousetrap)	C++17	100 / 100	937 ms	215632 KiB

mousetrap

//Autor: Bartłomiej Czarkowski
#include <bits/stdc++.h>
using namespace std;
#ifdef DEBUG
template<class A,class B>auto&operator<<(ostream&o,pair<A,B>p){return o<<'('<<p.first<<", "<<p.second<<')';}
template<class T>auto operator<<(ostream&o,T x)->decltype(x.end(),o){o<<'{';int i=0;for(auto e:x)o<<(", ")+2*!i++<<e;return o<<'}';}
#define debug(x...) cerr<<"["#x"]: ",[](auto...$){((cerr<<$<<"; "),...);}(x),cerr<<'\n'
#else
#define debug(...) {}
#endif

const int N = 1001000;
int n, a, b, m, q;
int par[N];
int son[N];
int cost[N];
int blk[N];
int stp[N];
int dp[N]; // ile żeby uwięzić i wyprowadzić do ojca
vector<int> v[N];

void dfs_dp(int x) {
	vector<int> war = {0, 0};
	for (int i : v[x]) {
		if (i == par[x]) {
			continue;
		}
		par[i] = x;
		dfs_dp(i);
		war.push_back(dp[i]);
	}
	nth_element(war.begin(), war.begin() + 1, war.end(), [&](int a, int b) {
		return a > b;
	});
	dp[x] = war[1] + war.size() - 2;
}

bool check(int wyn) {
	int x = m, nad = 1, usd = 0;
	while (x != q) {
		int ile = 0;
		for (int i : v[x]) {
			if (i != par[x] && i != son[x]) {
				if (dp[i] + blk[x] + usd > wyn) {
					++ile;
				}
			}
		}
		if (ile > nad) {
			return false;
		}
		nad -= ile;
		usd += ile;
		x = par[x];
		++nad;
	}
	return usd <= wyn;
}

int main() {
	scanf("%d%d%d", &n, &q, &m);
	for (int i = 1; i < n; ++i) {
		scanf("%d%d", &a, &b);
		v[a].push_back(b);
		v[b].push_back(a);
		++stp[a];
		++stp[b];
	}
	dfs_dp(q);
	int x = m;
	while (x != q) {
		son[par[x]] = x;
		x = par[x];
	}
	while (x != m) {
		x = son[x];
		blk[x] = blk[par[x]];
		for (int i : v[x]) {
			blk[x] += (i != par[x]) && (i != son[x]);
		}
	}
	int bp = -1, bk = max(n, 40), bs;
	while (bk - bp > 1) {
		bs = (bp + bk) / 2;
		if (check(bs)) {
			bk = bs;
		}
		else {
			bp = bs;
		}
	}
	printf("%d\n", bk);
	return 0;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:61:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   61 |  scanf("%d%d%d", &n, &q, &m);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:63:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   63 |   scanf("%d%d", &a, &b);
      |   ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 20 / 20
• Subtask 2: 25 / 25
• Subtask 3: 20 / 20
• Subtask 4: 35 / 35