【NOIP2016提高A组模拟7.15】修路

Description

The Solution

在每条边上减去两边城市的值，题目就转变成最小生成树了。
最小生成树？？<(￣3￣)> ，果断克鲁斯卡尔嘿嘿嘿

Code

#include 
#include 
#include  
#include 
#define fo(i,a,b) for (int i=a;i<=b;i++)
#define N 100005
using namespace std;
int n,m,Dad[N];
long long a[N],ans=0;
struct note
{
    int x,y;long long z;
}b[N];
bool cmp(note a,note b){return a.zint get(int x){return !Dad[x]?x:Dad[x]=get(Dad[x]);}
int main()
{
    scanf("%d%d",&n,&m);
    fo(i,1,n) scanf("%lld",&a[i]);
    fo(i,1,m)
    {
        scanf("%d%d%lld",&b[i].x,&b[i].y,&b[i].z);
        b[i].z-=a[b[i].x]+a[b[i].y];
    }
    sort(b+1,b+m+1,cmp);
    int tot=0;
    fo(i,1,m)
    {
        int xx=get(b[i].x),yy=get(b[i].y);
        if (xx!=yy)
        {
            tot++;
            ans+=b[i].z;
            Dad[xx]=yy;
        }
        if (tot>=n-1) break;
    }
    printf("%lld",ans);
    return 0;
}