Submission #59528

#	Time	Username	Problem	Language	Result	Execution time	Memory
59528		TAMREF	Islands (IOI08_islands)	C++11	80 / 100	1644 ms	132096 KiB

islands

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

typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,int> pli;

const int mx = 1e6 + 5;

struct Edg{
    int u, v, w;
    inline int oppo(int x){
        return u + v - x;
    }
} E[mx];

vector<int> G[mx];
int vis[mx];
bool dE[mx];
int num_cyc = 1; //greater than 1
int n;

int cv[mx], n_cv; //cycle vertex
int ce[mx], n_ce; //cycle edge weight
ll Vei[mx], n_vei;
ll Wei[mx], n_wei;

int dfs(int x){
    int cyc = 0, tcyc, u;
    vis[x] = 1;
    for(int &e : G[x]){
        if(dE[e]) continue;
        u = E[e].oppo(x);
        if(vis[u]){
            //printf("cycle detected - (%d->%d)\n",x,u);
            cyc = u;
            dE[e] = 1;
            ce[n_ce++] = E[e].w;
        }else{
            dE[e] = 1;
            tcyc = dfs(u);
            cyc |= tcyc;
            if(tcyc){
                ce[n_ce++] = E[e].w;
            }
        }
    }
    if(cyc){
        //printf("push %d in cv\n",x);
        cv[n_cv++] = x;
    }
    if(cyc == x){
        //printf("stopping cycle in %d\n",x);
        cyc = 0;
    }
    return cyc;
}

ll lans;
ll dfs_st(int x, int c){ //dfs for each subtrees in cycle
    vis[x] = c;
    int u, w;
    ll ans = 0, ans2 = 0, tmp;
    for(int &e : G[x]){
        u = E[e].oppo(x);
        w = E[e].w;
        if(vis[u] == 1){
            tmp = dfs_st(u, c) + w;
            if(tmp > ans) ans2 = ans, ans = tmp;
            else ans2 = max(ans2, tmp);
        }
    }
    lans = max(lans, ans + ans2); //local answer in subtree
    return ans;
}

inline void BackInsert(deque<pli>& d, pli p){
    while(!d.empty() && d.back() <= p) d.pop_back();
    d.push_back(p);
}

inline void OldPop(deque<pli>& d, int k){
    while(!d.empty() && d.front().second < k) d.pop_front();
}

ll calc(ll *Vw, int *E, ll *sE, int m){
    deque<pli> dq;
    ll lsum = E[0];
    ll ret = 0;

    for(int i = 0; i < m; i++){
        //printf("Vw = %lld,  E = %d, sE = %lld\n",Vw[i],E[i],sE[i]);
    }

    for(int i = 1; i < m; i++){
        BackInsert(dq, pli(Vw[i] + sE[i], i));
        lsum += E[i];
    }
    for(int i = 0; i < m; i++){
        OldPop(dq, i+1);
        ret = max(ret, Vw[i] - sE[i] + dq.front().first);
        BackInsert(dq, pli(Vw[i] + lsum + sE[i], i+m));
    }
    dq.clear();
    dq.shrink_to_fit();
    return ret;
}

ll dp_on_cycle(){
    int C = n_cv;
    ll lsum = 0;
    ll ans = 0;
    //give cycle-vertices their own number
    rotate(ce, ce+1, ce+C); //f**k
    for(int i = 0; i < C; i++){
        vis[cv[i]] = ++num_cyc;
        //printf("vertex : %d, clockwise - edge : %d\n",cv[i],ce[i]);
    }
    //clockwise
    for(int i = 0; i < C; i++){
        Vei[n_vei++] = dfs_st(cv[i], vis[cv[i]]);
        Wei[n_wei++] = lsum;
        lsum += ce[i];
    }
    ans = max(ans, calc(Vei, ce, Wei, n_ce));

    //inclockwise - reversing all the vectors
    lsum = 0;
    reverse(cv, cv + n_cv);
    reverse(Vei, Vei + n_vei);

    reverse(ce, ce + n_ce - 1);

    for(int i = 0; i < C; i++){
        //printf("vertex : %d, Inc ew : %d\n",cv[i],ce[i]);
        Wei[i] = lsum;
        lsum += ce[i];
    }

    ans = max(ans, calc(Vei, ce, Wei, n_ce));
    ans = max(ans, lans);
    //printf("dp result : %lld\n",ans);
    return ans;
}

void input(){
    cin >> n;
    for(int i = 1; i <= n; i++){
        cin >> E[i].v >> E[i].w;
        E[i].u = i;
        G[i].push_back(i);
        G[E[i].v].push_back(i);
    }
}

void debug(const char* S){
    /*
    for(int i = 1; i <= n; i++){
        if(G[i].size() > 1){
            //printf("deg[%d] = %d\n",i,G[i].size());
            for(int &e : G[i]){
                if(E[e].w > 90000000)
                    //printf("(%d, %d)\n",E[e].oppo(i),E[e].w);
            }
        }
    }
    */
    FILE *fp = fopen(S,"rt");
    ll correct;
    fscanf(fp,"%lld",&correct);
    printf("answer = %lld\n",correct);
}

int main(){
    //freopen("isl19g.in","rt",stdin);
    ios_base::sync_with_stdio(false);cin.tie(0);
    ll ans = 0;
    input();
    for(int i = 1; i <= n; i++){
        if(!vis[i]){
            n_cv = n_ce = n_wei = n_vei = 0;
            dfs(i);
            lans = 0;
            ans += dp_on_cycle();
        }
    }
    cout << ans << '\n';
    //debug("isl19g.out");
}

Compilation message (stderr)

islands.cpp: In function 'void debug(const char*)':
islands.cpp:170:11: warning: ignoring return value of 'int fscanf(FILE*, const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     fscanf(fp,"%lld",&correct);
     ~~~~~~^~~~~~~~~~~~~~~~~~~~

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