51nod 1640 天气晴朗的魔法

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<map>
#include<vector>
#include<cstring>
#include<cmath>
using namespace std;
typedef long long ll;
const int inf =0x3f3f3f3f;
const double  pi = acos(-1.0);
const int N = 3e5 + 10;
int root[N];
struct node
{
    int x, y;
    ll w;
} p[N];
int Find(int x)
{
    return x == root[x]?x:root[x] = Find(root[x]);
}
int cmp1(node a, node b)
{
    return a.w<b.w;
}
int cmp2(node a, node b)
{
    return a.w>b.w;
}
int main()
{
    int n, m;
    scanf("%d%d", &n, &m);
    for(int i = 0; i<m; i++)
    {
        scanf("%d%d%I64d", &p[i].x, &p[i].y, &p[i].w);
    }
    for(int i = 0; i<=n; i++)
        root[i] = i;
    sort(p, p+m, cmp1);
    int k, num = 0;
    ll last = -inf*100LL;
    for(int i = 0; i<m; i++)
    {
        int a = Find(p[i].x), b = Find(p[i].y);
        if(a!=b)
        {
            num++;
            last = max(last, p[i].w);
            root[a] = b;
        }
        if(num == n-1)
        {
            break;
        }
    }

    for(int i = 0; i<=n; i++)
        root[i] = i;
    for(int i = 0; i<m; i++)
    {
        if(p[i].w>last)
        {
            k = i;
            break;
        }
    }
    sort(p, p+k, cmp2);
    ll ans = 0;
    num = 0;
    for(int i = 0; i<k; i++)
    {
        int a = Find(p[i].x), b = Find(p[i].y);
        if(a!=b)
        {
            num++;
            ans += p[i].w;
            root[a] = b;
        }
        if(num == n-1)
            break;
    }
    cout<<ans<<endl;
    return 0;
}