| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 395671 | MarcoMeijer | Islands (IOI08_islands) | C++14 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define INF 1e18
#define EPS 1e-9
#define pb push_back
#define popb pop_back
#define fi first
#define se second
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
// input
template<class T> void IN(T& x) {cin >> x;}
template<class H, class... T> void IN(H& h, T&... t) {IN(h); IN(t...); }
// output
template<class T1, class T2> void OUT(const pair<T1,T2>& x);
template<class T> void OUT(const vector<T>& x);
template<class T> void OUT(const T& x) {cout << x;}
template<class H, class... T> void OUT(const H& h, const T&... t) {OUT(h); OUT(t...); }
template<class T1, class T2> void OUT(const pair<T1,T2>& x) {OUT(x.fi,' ',x.se);}
template<class T> void OUT(const vector<T>& x) {RE(i,x.size()) OUT(i==0?"":" ",x[i]);}
template<class... T> void OUTL(const T&... t) {OUT(t..., "\n"); }
template<class H> void OUTLS(const H& h) {OUTL(h); }
template<class H, class... T> void OUTLS(const H& h, const T&... t) {OUT(h,' '); OUTLS(t...); }
// dp
template<class T> bool ckmin(T&a, T&b) { bool bl = a > b; a = min(a,b); return bl;}
template<class T> bool ckmax(T&a, T&b) { bool bl = a < b; a = max(a,b); return bl;}
void program();
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
program();
}
//===================//
// begin program //
//===================//
const int MX = 1e6+8;
const int N = (1<<20);
int n, edges;
int l[MX];
vii adj[MX];
// finding cycles
bitset<MX> visited;
int cycleStart;
int skippedEdge = -1;
vii cycle;
bool dfsVisit(int u, int pe) {
if(visited[u]) {
cycleStart = u;
skippedEdge = pe;
return true;
}
bool res = false;
visited[u] = 1;
RE(i,adj[u].size()) {
if(adj[u][i].se == pe || adj[u][i].se == skippedEdge) continue;
if(!dfsVisit(adj[u][i].fi, adj[u][i].se^1)) continue;
cycle.pb({adj[u][i].fi, l[adj[u][i].se/2]});
res = u != cycleStart;
}
return res;
}
// finding depth
ll curBest = 0;
void combine(lll& x, ll y) {x = {max(x.fi,y), max(min(x.fi,y),x.se)};}
bitset<MX> visited2;
ll dfsDepth(int u) {
lll p = {0,0};
visited2[u] = 1;
RE(i,adj[u].size()) {
if(visited2[adj[u][i].fi]) continue;
p = combine(p,l[adj[u][i].se/2] + dfsDepth(adj[u][i].fi));
}
curBest = max(curBest, p.fi + p.se);
return p.fi;
}
void program() {
IN(n);
RE1(b,n) {
int a; IN(a,l[b-1]);
adj[a].pb({b,edges++});
adj[b].pb({a,edges++});
}
RE1(i,n) adj[i].shrink_to_fit();
ll ans = 0;
RE1(i,n) {
if(visited[i]) continue;
// find the cycle
curBest = 0;
cycle.clear(); cycle.shrink_to_fit();
dfsVisit(i,-1);
// fill a, b and c
ll m = cycle.size(), totB = 0;
FOR(u,cycle) totB += u.se;
ll curB = totB;
ll bestSum1 = -INF, bestSum2 = -INF;
REV(i,0,m) {
curB -= cycle[i].se;
visited2[cycle[i].fi] = 0;
visited2[cycle[(i+1+m)%m].fi] = 1;
visited2[cycle[(i-1+m)%m].fi] = 1;
ll C = dfsDepth(cycle[i].fi);
curBest = max(curBest , bestSum1 - curB + C);
curBest = max(curBest , totB + bestSum2 + curB + C);
bestSum1 = max(bestSum1, curB + C);
bestSum2 = max(bestSum2, -curB + C);
}
ans += curBest;
}
OUTL(ans);
}