Submission #161248

#	Time	Username	Problem	Language	Result	Execution time	Memory
161248		Juney	Race (IOI11_race)	C++14	100 / 100	1410 ms	37208 KiB

race

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

#define fi first
#define se second
#define all(x) ((x).begin(), (x).end())

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int MAXN = 2e5 + 5;
const int INF = 1e9;
const ll MOD = 1e9 + 7;

int N, sz[MAXN], ans, K;
vector<pii> G[MAXN];
bool del[MAXN];
map<int, int> mp;

int szdfs(int cur, int par) {
	sz[cur] = 1;
	for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) sz[cur] += szdfs(i.fi, cur);
	return sz[cur];
}

int cdfs(int cur, int par, int cap) {
	for(auto i : G[cur]) if(!del[i.fi] && i.fi != par && sz[i.fi] > cap) return cdfs(i.fi, cur, cap);
	return cur;
}

void dfs(int cur, int par, int dis, int cnt) {
	if(dis > K) return;
	if(mp.find(K - dis) != mp.end()) ans = min(ans, mp[K - dis] + cnt);
	for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) dfs(i.fi, cur, dis + i.se, cnt+1);
}

void add(int cur, int par, int dis, int cnt) {
	if(dis > K) return;
	if(mp.find(dis) == mp.end()) mp[dis] = cnt;
	else mp[dis] = min(mp[dis], cnt);
	for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) add(i.fi, cur, dis + i.se, cnt+1);
}

void solve(int cur) {
	mp.clear();
	mp[0] = 0;
	for(auto i : G[cur]) if(!del[i.fi]) dfs(i.fi, cur, i.se, 1), add(i.fi, cur, i.se, 1);
}

void decompose(int root, int par) {
	int cap = szdfs(root, 0);
	int cen = cdfs(root, 0, cap / 2);
	del[cen] = 1;
	solve(cen);
	for(auto i : G[cen]) if(!del[i.fi]) decompose(i.fi, cen);
}

int best_path(int _N, int _K, int H[][2], int L[]) {
	N = _N; K = _K;
	for(int i=0; i<N-1; i++) {
		int a = H[i][0]+1, b = H[i][1]+1, c = L[i];
		G[a].push_back(pii(b, c)); G[b].push_back(pii(a, c));
	}
	ans = 1e9;
	decompose(1, 0);
	if(ans == 1e9) return -1;
	return ans;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57