poj 2421 constructing roads

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>

using namespace std;

struct node
{
    int x,y,dis;
}Edge[100001];
int fa[1001],N,i,a,tot,j,k;
bool cmp(node a,node b)
{
    return a.dis<b.dis;
}
int find_fa(int k)
{
    return fa[k]==k?k:find_fa(fa[k]);
}
int main()
{
    cin>>N;
    int a;
    for(i=1;i<=N;++i)
    {
        for(j=1;j<=N;++j)
        {
            cin>>a;
            if(a)
            {
                tot++;
                Edge[tot].x=i;
                Edge[tot].y=j;
                Edge[tot].dis=a;
            }
        }
    }
    int Q;
    cin>>Q;
    int b,c;
    for(i=1;i<=N;++i)
    fa[i]=i;
    int h=0;
    while(Q--)
    {
        cin>>b>>c;
        tot++;
        Edge[tot].x=b;
        Edge[tot].y=c;
        Edge[tot].dis=0;
    }
    sort(Edge+1,Edge+1+tot,cmp);
    int ans=0;
    for(i=1;i<=tot;++i)
    {
        int x,y;
        x=find_fa(Edge[i].x);
        y=find_fa(Edge[i].y);
        if(x!=y)
        {
            fa[y]=x;
            h++;
            ans+=Edge[i].dis;
            if(h==N-1)
            break;
        }
    }
    cout<<ans;
    return 0;
}