Kruskal 70 ,求助

用的Kruskal,先放代码

//#include<bits/stdc++.h>
#include<iostream>
#include<iomanip>
#include<cstdio>
#include<stack>
#include<list>
#include<map>
#include<set>
#include<cmath>
#include<cstring>
#include<queue>
#include<algorithm>
#include<vector>
#define ll long long
#define reg register int
#define gc getchar()
#define MAXN 20001//边的数量 
#define MAXM 5001 //顶点数量 

using namespace std;

int m,n;
int fth[MAXM];
ll sum;

inline ll read(void);

inline int find(int x){

    if(fth[x]==x) return x;
    fth[x]=find(fth[x]);
    return fth[x];

}

struct edge{
    int from,to,len;
}a[MAXN];

inline bool cmp( edge a , edge b );

int main(void){

    n=read();//节点 
    m=read();//无向边 
    for(reg i=1;i<=m;i++) {
        a[i].from = read() ;
        a[i].to = read() ;
        a[i].len = read() ;
    }
    //在这里读入所有无向边

    sort(a+1,a+1+m,cmp);
    //把所有边依照边长进行排序

    for(reg i=1;i<=n;i++) fth[i]=i;
    //并查集初始化
    int k=0;
    int from_,to_;
    for(reg i=1;i<=m;i++){

        from_=find(a[i].from);
        to_=find(a[i].to);

        if(from_!=to_){

            //选择这一条边 
            k++;
            fth[from_]=to_;
            sum+=a[i].len;
            if(k==n-1) break; 

        }
    }

    if(k<n-1) cout<<"orz"<<endl;
    else cout<<sum<<endl;

    return 0;

}

inline ll read(void){
    ll x=0,f=0;
    char ch=gc;
    while(!isdigit(ch))
             f|=(ch=='-'),ch=gc;
    while(isdigit(ch))
             x=(x<<1)+(x<<3)+(ch^48),ch=gc;
        return f ? -x : x ;
}

inline bool cmp( edge a , edge b ){
    return a.len < b.len ;
}

8,9是WA 10是MLE

求应该怎样优化