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May 2, 2017 17:20
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//Estacao - Seletiva IOI - 2015 | |
#include <bits/stdc++.h> | |
#define N 2*100050 | |
using namespace std; | |
int n, m, grau[N], save[N], nivel[N]; | |
vector<int> grafo[N], lista, P, I; | |
int solve() | |
{ | |
for(int i = 0; i<lista.size(); i++) | |
{ | |
vector<int> par, impar; | |
int x = lista[i]; | |
for(int j = 0; j<grafo[x].size(); j++) | |
{ | |
int v = grafo[x][j]; | |
grau[v] --; | |
if(grau[v] == 0) | |
{ | |
lista.push_back(v); | |
if(v%2 == 0)par.push_back(v); | |
else impar.push_back(v); | |
} | |
} | |
if(x%2 == 0) | |
{ | |
if(impar.size() > 0) | |
{ | |
for(int i = 0; i<impar.size(); i++) | |
{ | |
int k = impar[i]; | |
nivel[k] = nivel[x] + 1; | |
} | |
for(int i = 0; i<par.size(); i++) | |
{ | |
int k = par[i]; | |
nivel[k] = nivel[x] + 2; | |
} | |
} | |
} | |
else | |
{ | |
if(par.size() > 0) | |
{ | |
for(int i = 0; i<par.size(); i++) | |
{ | |
int k = par[i]; | |
nivel[k] = nivel[x] + 1; | |
} | |
for(int i = 0; i<impar.size(); i++) | |
{ | |
int k = impar[i]; | |
nivel[k] = nivel[x] + 2; | |
} | |
} | |
} | |
} | |
int cont = 2; | |
for(int i = 1; i<=2*n; i++)cont = max(cont, nivel[i]); | |
return cont; | |
} | |
int main() | |
{ | |
cin>>n>>m; | |
for(int i = 1; i<=m; i++) | |
{ | |
int a, o, b; | |
cin>>a>>o>>b; | |
if(o == -1) swap(a, b); | |
grafo[a].push_back(b); | |
grau[b] ++; | |
save[b]++; | |
} | |
for(int i = 1; i<=2*n; i++) | |
{ | |
if(grau[i] == 0 && grafo[i].size() >0) | |
lista.push_back(i); | |
} | |
for(int i = 0; i<lista.size(); i++) | |
{ | |
int x = lista[i]; | |
if(x%2 == 0) P.push_back(x); | |
else I.push_back(x); | |
} | |
if(I.size() > 0) | |
{ | |
for(int i = 0; i<P.size(); i++) nivel[P[i]] = 2; | |
for(int i = 0; i<I.size(); i++) nivel[I[i]] = 1; | |
} | |
else | |
for(int i = 0; i<P.size(); i++) | |
nivel[P[i]] = 1; | |
int a = solve(); | |
lista.clear(); | |
for(int i = 1; i<=2*n; i++) grau[i] = save[i]; | |
for(int i = 1; i<=2*n; i++) | |
{ | |
if(grau[i] == 0 && grafo[i].size() >0) | |
lista.push_back(i); | |
} | |
if(P.size() > 0) | |
{ | |
for(int i = 0; i<P.size(); i++) nivel[P[i]] = 1; | |
for(int i = 0; i<I.size(); i++) nivel[I[i]] = 2; | |
} | |
else | |
for(int i = 0; i<I.size(); i++) nivel[I[i]] = 1; | |
int b = solve(); | |
cout<<min(a, b)<<"\n"; | |
} |
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