全wa求助

#include<cstring>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<algorithm>
using namespace std;
inline int read()
{
    register int X=0;register char ch=0;bool flag=0;
    for(;!isdigit(ch);ch=getchar()) if(ch=='-') flag=1;
    for(;isdigit(ch);ch=getchar()) X=(X<<3)+(X<<1)+ch-'0';
    return (flag ? -X : X);
}
inline void write(int x)
{
     if(x>9) write(x/10);
     putchar(x%10+'0');
}
int fa[500001],n,m,ans,cnt;
int find(int x)
{
	return fa[x]==x ? x : (fa[x]=find(fa[x]));
}
struct edge
{
	int u,v,val;
}e[20000001];
bool cmp(edge xx,edge yy)
{
	if(xx.val < yy.val)
		return 1;
	else if(xx.val == yy.val)
		return xx.u<yy.u;
	return 0;
}
int main()
{
	n=read(),m=read();
	for(int i=1;i<=n;i++) fa[i]=i;
	for(int i=1;i<=m;i++)
		e[i].u=read(),e[i].v=read(),e[i].val=read();
	sort(e+1,e+n+1,cmp);
	for(int i=1;i<=m;i++)
	{
		int u=e[i].u,v=e[i].v,val=e[i].val;
		int fu=find(u),fv=find(v);
		if(fu != fv)
			fa[fu]=fv;
		ans+=val,cnt++;
	}
	printf("%d\n",ans);
}