Submission #92271

#	Time	Username	Problem	Language	Result	Execution time	Memory
92271		Retro3014	Islands (IOI08_islands)	C++17	100 / 100	1456 ms	107532 KiB

islands

#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>

using namespace std;
#define MAX_N 1000000
typedef long long ll;

int N;
struct S{
    int idx;
    int data;
};
vector<S> gp[MAX_N+1];
int a, b;

struct C{
    ll a, b;
};
deque<C> cycle;
bool vst[MAX_N+1];

int num[MAX_N+1];
ll len[MAX_N+1];
deque<int> leaf;
ll m[MAX_N+1][3];
ll ans=0;
vector<S> gp2;

int main(){
    scanf("%d", &N);
    for(int i=1; i<=N; i++){
        scanf("%d%d", &a, &b);
        gp[i].push_back((S){a, b}); num[i]++;
        gp[a].push_back((S){i, b}); num[a]++;
    }
    for(int i=1; i<=N; i++){
        if(num[i]==1){
            leaf.push_back(i);
        }
    }
    while(!leaf.empty()){
        int now=leaf.front(); leaf.pop_front();
        vst[now]=true;
        m[now][0]=max(m[now][0], m[now][1]+m[now][2]);
        for(int i=0; i<gp[now].size(); i++){
            if(!vst[gp[now][i].idx]){
                len[gp[now][i].idx]=max(len[gp[now][i].idx], len[now]+(ll)gp[now][i].data);
                m[gp[now][i].idx][0]=max(m[gp[now][i].idx][0], m[now][0]);
                if(len[now]+(ll)gp[now][i].data>m[gp[now][i].idx][1]){
                    m[gp[now][i].idx][2]=m[gp[now][i].idx][1];
                    m[gp[now][i].idx][1]=len[now]+(ll)gp[now][i].data;
                }else if(len[now]+gp[now][i].data>m[gp[now][i].idx][2]){
                    m[gp[now][i].idx][2]=len[now]+(ll)gp[now][i].data;
                }
                num[gp[now][i].idx]--;
                if(num[gp[now][i].idx]==1){
                    leaf.push_back(gp[now][i].idx);
                }
            }
        }
    }
    ll ans2=0;
    ll sum=0, m1, m2;
    int t;
    for(int i=1; i<=N; i++){
        if(!vst[i]){
            for(int j=0; j<gp[i].size(); j++){
                if(!vst[gp[i][j].idx]){
                    gp2.push_back(gp[i][j]);
                }
            }
            while(!gp[i].empty())    gp[i].pop_back();
            while(!gp2.empty()){
                gp[i].push_back(gp2.back()); gp2.pop_back();
            }
        }
    }
    for(int i=1; i<=N; i++){
        t=i;
        if(!vst[i]){
            cycle.push_front({gp[i][1].idx, (ll)gp[i][1].data});
            while(1){
                vst[t]=true;
                if(vst[gp[t][0].idx]){
                    if(vst[gp[t][1].idx]){
                        break;
                    }
                    cycle.push_front({t, (ll)gp[t][1].data});
                    t=gp[t][1].idx;
                }else{
                    cycle.push_front({t, (ll)gp[t][0].data});
                    t=gp[t][0].idx;
                }
            }
            ans2=0; sum=0;
            for(int j=0; j<cycle.size(); j++){
                sum+=cycle[j].b;
                ans2=max(ans2, max(m[cycle[j].a][0], m[cycle[j].a][1]+m[cycle[j].a][2]));
            }
            /*while(!c.empty()){
             S now = c.back(); c.pop_back();
             ans2=max(ans2, max(m[now.idx][0], m[now.idx][1]+m[now.idx][2]));
             sum+=now.data;
             cycle.push_back({now.data, len[now.idx]});
             }*/
            m1 = m2 = 0;
            while(!cycle.empty()){
                C now = cycle.back(); cycle.pop_back();
                ans2=max(ans2, max(len[now.a], max(m1+len[now.a], m2+len[now.a])));
                m1=max(m1+now.b, now.b+len[now.a]);
                m2=max(m2-now.b, sum-now.b+len[now.a]);
            }
            ans+=ans2;
        }
    }
    printf("%lld", ans);
    return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:47:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<gp[now].size(); i++){
                      ~^~~~~~~~~~~~~~~
islands.cpp:69:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(int j=0; j<gp[i].size(); j++){
                          ~^~~~~~~~~~~~~
islands.cpp:98:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(int j=0; j<cycle.size(); j++){
                          ~^~~~~~~~~~~~~
islands.cpp:32:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &N);
     ~~~~~^~~~~~~~~~
islands.cpp:34:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &a, &b);
         ~~~~~^~~~~~~~~~~~~~~~

• 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: 10 / 10
• Subtask 9: 10 / 10