Submission #217679

#	Time	Username	Problem	Language	Result	Execution time	Memory
217679		mhy908	Islands (IOI08_islands)	C++14	80 / 100	1315 ms	131076 KiB

islands

#include <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define F first
#define S second
using namespace std;
typedef long long LL;
typedef pair<int, int> pii;
const LL llinf=1987654321987654321;

int n;
LL ret, ans;
list<pii> link[1000010];
int cyc[1000010], re;
LL sum[1000010];
bool ch[1000010];

void chdfs(int num, int par1, int par2){
    ch[num]=true;
    for(auto i:link[num]){
        if(i.F==par1||i.F==par2)continue;
        chdfs(i.F, num, par2);
    }
}

LL get_cyc(int num, int par){
    if(ch[num]){
        cyc[re]=num;
        sum[re++]=0;
        return 0;
    }
    ch[num]=true;
    int t=0;
    for(auto i:link[num]){
        if(i.F==par&&!t){
            t++;
            continue;
        }
        LL temp=get_cyc(i.F, num)+i.S;
        if(temp>=0){
            cyc[re]=num;
            sum[re++]=temp;
            if(cyc[0]==num)return -llinf;
            return temp;
        }
    }
    return -llinf;
}

LL get_maxd(int num, int par1, int par2){
    LL ret2=0;
    for(auto i:link[num]){
        if(i.F==par1||i.F==par2)continue;
        LL temp=get_maxd(i.F, num, num)+i.S;
        ret=max(ret, ret2+temp);
        ret2=max(ret2, temp);
    }
    return ret2;
}

LL solve(int num){
    re=0; ret=0;
    get_cyc(num, 0);
    chdfs(cyc[0], 0, cyc[0]);
    LL max1=llinf, max2=-llinf, dia=sum[--re];
    for(int i=0; i<re; i++){
        LL tmp=get_maxd(cyc[i], cyc[(i+re-1)%re], cyc[(i+1)%re]);
        ret=max(ret, sum[i]+tmp-max1);
        ret=max(ret, dia-sum[i]+tmp+max2);
        max2=max(max2, sum[i]+tmp);
        max1=min(max1, sum[i]-tmp);
    }
    return ret;
}

int main(){
    scanf("%d", &n);
    for(int i=1; i<=n; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        link[i].pb(mp(a, b));
        link[a].pb(mp(i, b));
    }
    for(int i=1; i<=n; i++){
        if(ch[i])continue;
        ans+=solve(i);
    }
    printf("%lld", ans);
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:77:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~
islands.cpp:80:14: 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: 0 / 10
• Subtask 9: 0 / 10