Submission #635436

#	Time	Username	Problem	Language	Result	Execution time	Memory
635436		S2speed	LOSTIKS (INOI20_lostiks)	C++17	59 / 100	2089 ms	247404 KiB

Main

#include<bits/stdc++.h>

using namespace std;

#pragma GCC optimize ("Ofast")

#define sze(x) (int)(x.size())
typedef long long ll;
typedef pair<ll , ll> pll;
typedef pair<int , int> pii;
typedef pair<pii , int> piii;

const ll maxn = (1 << 20) + 17 , inf = 2e8;

int n , s , t;
pii adj[maxn << 1];
vector<piii> ed;
int dg[maxn] , st[maxn] , ft[maxn] , x[maxn];
int dis[22][maxn];
int bfs[maxn] , sz = 0;
int g[maxn] , k[22] , d[22] , e[22] , f[22][22] , dp[maxn][22] , ind[22];

void rBFS(int r , int h){
	sz = 0;
	dis[h][r] = 0;
	g[r] = 0;
	bfs[sz++] = r;
	int x = 0;
	while(x < sz){
		int v = bfs[x++];
		for(int e = st[v] ; e < ft[v] ; e++){
			pii p = adj[e];
			int i = p.first , t = p.second;
			if(dis[h][i] < dis[h][v] + 1) continue;
			g[i] = g[v];
			if(t != -1){
				g[i] ^= (1 << t);
				d[t] = v;
			}
			dis[h][i] = dis[h][v] + 1;
			bfs[sz++] = i;
		}
	}
	return;
}

void BFS(int r , int h){
	sz = 0;
	dis[h][r] = 0;
	g[r] = 0;
	bfs[sz++] = r;
	int x = 0;
	while(x < sz){
		int v = bfs[x++];
		for(int e = st[v] ; e < ft[v] ; e++){
			pii p = adj[e];
			int i = p.first , t = p.second;
			if(dis[h][i] < dis[h][v] + 1) continue;
			dis[h][i] = dis[h][v] + 1;
			bfs[sz++] = i;
		}
	}
	return;
}

int main(){
	ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);

	memset(dp , 63 , sizeof(dp));
	memset(dis , 63 , sizeof(dis));
	cin>>n>>s>>t; s--; t--;
	int m = 0;
	for(int i = 1 ; i < n ; i++){
		int v , u , w;
		cin>>v>>u>>w; v--; u--; w--;
		dg[v]++; dg[u]++;
		if(w != -1){
			k[m] = w;
			ed.push_back({{v , u} , m});
			m++;
		} else {
			ed.push_back({{v , u} , -1});
		}
	}
	x[0] = st[0] = 0; ft[0] = dg[0];
	for(int i = 1 ; i < n ; i++){
		x[i] = st[i] = ft[i - 1]; ft[i] = st[i] + dg[i];
	}
	for(auto p : ed){
		int v = p.first.first , u = p.first.second , w = p.second;
		adj[x[v]++] = {u , w}; adj[x[u]++] = {v , w};
	}
	rBFS(s , m);
	if(g[t] == 0){
		cout<<dis[m][t]<<'\n';
		return 0;
	}
	for(int j = 0 ; j < m ; j++){
		e[j] = g[k[j]] | g[d[j]];
		BFS(d[j] , j);
		if(e[j] == 0){
			dp[(1 << j)][j] = dis[m][k[j]] + dis[j][k[j]];
		}
	}
	for(int i = 0 ; i < m ; i++){
		for(int j = 0 ; j < m ; j++){
			f[i][j] = dis[i][k[j]] + dis[j][k[j]];
		}
	}
	int lm = (1 << m);
	for(int mask = 3 ; mask < lm ; mask++){
		int bp = 0;
		for(int j = 0 ; j < m ; j++){
			if(mask & (1 << j)) ind[bp++] = j;
		}
		if(bp == 1) continue;
		for(int jj = 0 ; jj < bp ; jj++){
			int j = ind[jj];
			if((e[j] & mask) != e[j]) continue;
			int h = inf , msk = mask ^ (1 << j);
			for(int ii = 0 ; ii < bp ; ii++){
				int i = ind[ii];
				if(i == j) continue;
				h = min(h , dp[msk][i] + f[i][j]);
			}
			dp[mask][j] = h;
		}
	}
	int ans = inf;
	for(int mask = 1 ; mask < lm ; mask++){
		if((g[t] & mask) != g[t]) continue;
		int h = inf;
		for(int i = 0 ; i < m ; i++){
			if(!(mask & (1 << i))) continue;
//			cout<<mask<<' '<<i<<'\n';
			h = min(h , dp[mask][i] + dis[i][t]);
		}
		ans = min(ans , h);
	}
	cout<<(ans == inf ? -1 : ans)<<'\n';
	return 0;
}

Compilation message (stderr)

Main.cpp: In function 'void BFS(int, int)':
Main.cpp:57:22: warning: unused variable 't' [-Wunused-variable]
   57 |    int i = p.first , t = p.second;
      |                      ^

• Subtask 1: 23 / 23
• Subtask 2: 36 / 36
• Subtask 3: 0 / 41