Submission #362880

#	Time	Username	Problem	Language	Result	Execution time	Memory
362880		David_M	Race (IOI11_race)	C++17	100 / 100	487 ms	79212 KiB

race

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

const int N=200005;
int sz[N], e[N], z1[N], z2[N], o, k, K, Ans=N;
vector <pair<int, int> > v[N];
map<int, int> m[N];

void solve(int x=0, int pa=0){
	
	sz[x]=1;
	int mx=0, Y, D;
	
	for (auto [y,d]:v[x]){
		if(y==pa)continue;
		solve(y, x);
		sz[x]+=sz[y];
		if(sz[y]>mx) mx=sz[y], Y=y, D=d;
	}
	
	if(sz[x]==1) e[x]=o++;
	else z1[x]=z1[Y]+D, z2[x]=z2[Y]+1, e[x]=e[Y];
	m[e[x]][0-z1[x]]=0-z2[x];
	
	for (auto [y,d]:v[x]){
		if(y==pa||y==Y)continue;
		for(auto [kk,ans]:m[e[y]]){
			k=kk+d+z1[y]+z1[x];
			ans+=1+z2[y]+z2[x];
			if(m[e[x]].find(K-k)!=m[e[x]].end()) Ans=min(Ans, ans+m[e[x]][K-k]);
		}
		for(auto [kk,ans]:m[e[y]]){
			k=kk+d+z1[y]-z1[x];
			ans+=1+z2[y]-z2[x];
			if(m[e[x]].find(k)==m[e[x]].end() || m[e[x]][k]>ans) m[e[x]][k]=ans;
		}
	}
	if(m[e[x]].find(K-z1[x])!=m[e[x]].end())Ans=min(Ans,z2[x]+m[e[x]][K-z1[x]]);
}

int best_path(int n, int k, int H[][2], int L[]){
	K=k;
	for (int i=0; i<n-1; i++)
		v[H[i][0]].push_back({H[i][1],L[i]}),
		v[H[i][1]].push_back({H[i][0],L[i]});
	
	solve();
	
	return (Ans==N)?-1:Ans;
}

Compilation message (stderr)

race.cpp: In function 'void solve(int, int)':
race.cpp:27:11: warning: 'Y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   27 |   if(y==pa||y==Y)continue;
      |      ~~~~~^~~~~~
race.cpp:23:18: warning: 'D' may be used uninitialized in this function [-Wmaybe-uninitialized]
   23 |  else z1[x]=z1[Y]+D, z2[x]=z2[Y]+1, e[x]=e[Y];
      |             ~~~~~^~

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