Submission #570852

#	Time	Username	Problem	Language	Result	Execution time	Memory
570852		amukkalir	Islands (IOI08_islands)	C++17	64 / 100	375 ms	131072 KiB

islands

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

#define pii pair<int, int> 
#define fi first 
#define se second 
#define pb push_back

const int nax = 1e6; 
int n; 
int p[nax+5]; 
bool vis[nax+5]; 
long long c[nax+5]; 
long long val[nax+5]; 
vector<pii> adj[nax+5]; 
vector<int> cyc[nax+5]; 
vector<pii> edg; 

void gp(int u, int par, int ls=0) {
    p[u] = par; 
    for(pii t : adj[u]) {
        int v = t.fi; 
        int e = t.se; 
        if(e == ls) continue; 

        if(p[v] == 0) {
            gp(v, par, e); 
        } else {
            cyc[par].push_back(e); 
        }
    }
}

bool fc(int u, int go, int ls) {
    if(u == go) return true; 

    for(pii t : adj[u]) {
        int v = t.fi; 
        int e = t.se; 
        if(e == ls) continue; 
        
        bool ok = fc(v, go, e); 
        if(ok) {
            vis[u] = true; 
            vis[v] = true; 
            if(edg[e].fi != u) swap(edg[e].fi, edg[e].se); 
            cyc[p[go]].push_back(e); 
            return true; 
        } 
    }

    return false; 
}

long long trav(int u) {
    if(val[u] != -1) return val[u]; 

    vis[u] = true; 
    long long res = 0; 
    for(pii t : adj[u]) {
        int v = t.fi; 
        int e = t.se; 
        if(!vis[v]) {
            res = max(res, c[e] + trav(v)); 
        }
    }

    return val[u] = res; 
}

int main () {
    scanf("%d", &n); 

    edg.pb({0,0}); 
    for(int i=1; i<=n; i++) {
        long long l, j;         
        scanf("%lld %lld", &j, &l); 

        c[i] = l; 
        adj[j].pb({i,i}); 
        adj[i].pb({j,i}); 
        edg.pb({i,j}); 
        val[i] = -1; 
    }

    long long ans = 0; 
    for(int i=1; i<=n; i++) {
        if(p[i] == 0) {
            gp(i,i); 
            cyc[i].pop_back(); 
            fc(edg[cyc[i][0]].se, edg[cyc[i][0]].fi, cyc[i][0]); 

            long long opt = 0; 

            //priority_queue<long long> pq; 
            deque<pair<long long, int>> dq; 

            long long dpq = 0; 
            long long sum = 0; 
            int sz = cyc[i].size(); 
            int cnt = 0; 

            for(int j=0; j<sz; j++) {
                int e = cyc[i][j]; 
                swap(edg[e].fi, edg[e].se); 
                sum += c[e]; 
                
                if(j+1 < sz) {
                    long long temp = sum + trav(edg[e].se); 
                    while(!dq.empty() && dq.back().fi <= temp) dq.pop_back(); 
                    dq.push_back({temp,cnt++}); 
                }
            }

            for(int j=0; j<sz; j++) {
                int e = cyc[i][j]; 
                int u = edg[e].fi; 
                opt = max(opt, trav(u) + dq.front().fi + dpq); 
                dpq -= c[e]; 
                long long temp = trav(u) + sum - c[e] - dpq; 

                while(!dq.empty() && dq.front().se <= cnt-sz) dq.pop_front(); 
                while(!dq.empty() && dq.back().fi <= temp) dq.pop_back(); 
                dq.push_back({temp,cnt++}); 
            }

            ans += opt; 
        }
    }

    printf("%lld", ans); 
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:72:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   72 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
islands.cpp:77:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   77 |         scanf("%lld %lld", &j, &l);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 27 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 0 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10