[学习笔记]三元环

#include<bits/stdc++.h>
#define reg register int
#define il inline
#define numb (ch^‘0‘)
using namespace std;
typedef long long ll;
il void rd(int &x){
    char ch;x=0;bool fl=false;
    while(!isdigit(ch=getchar()))(ch==‘-‘)&&(fl=true);
    for(x=numb;isdigit(ch=getchar());x=x*10+numb);
    (fl==true)&&(x=-x);
}
namespace Miracle{
const int N=100000+5;
int n,m;
int a[N];
struct node{
    int nxt,to;
}e[250000+5];
int hd[N],cnt;
void add(int x,int y){
    e[++cnt].nxt=hd[x];
    e[cnt].to=y;
    hd[x]=cnt;
}
int du[N];
int b[250000+5][2];
ll ans=0;
int vis[N];
int main(){
    rd(n);rd(m);
    for(reg i=1;i<=n;++i) rd(a[i]);
    for(reg i=1;i<=m;++i){
        rd(b[i][0]);rd(b[i][1]);
        ++du[b[i][0]];++du[b[i][1]];
    }
    for(reg i=1;i<=m;++i){
        int x=b[i][0],y=b[i][1];
        if(du[x]<du[y]||(du[x]==du[y]&&x<y)) swap(x,y);
        add(x,y);
    }
    for(reg x=1;x<=n;++x){
        for(reg i=hd[x];i;i=e[i].nxt){
            int y=e[i].to;
            vis[y]=x;
        }
        for(reg i=hd[x];i;i=e[i].nxt){
            int y=e[i].to;
            for(reg j=hd[y];j;j=e[j].nxt){
                int z=e[j].to;
                if(vis[z]==x) ans+=max(max(a[x],a[y]),a[z]);
            }
        }
    }
    printf("%lld",ans);
    return 0;
}

}
signed main(){
    Miracle::main();
    return 0;
}

/*
   Author: *Miracle*
   Date: 2019/3/6 14:12:52
*/