poj 1258 Agri-Net

kruskal

#include<iostream>
#include<algorithm>
#include<cstdio>
using namespace std;
#define maxn 200
int a[maxn][maxn];
int par[maxn];
int n,len;
int num;
struct node
{
    int x;
    int y;
    int w;
};
node e[maxn * maxn / 2];
int cmp(const node& a,const node &b)
{
    return a.w < b.w;
}
int Find(int k)
{
    if(par[k] == k)   return k;
    par[k] = Find(par[k]);
    return par[k];
}
void Merge(int x,int y)
{
    int a = Find(x);
    int b = Find(y);
    if(a != b)
    {
        par[a] = b;
    }
}

void kruskal()
{

    while(cin>>n)
    {
        for(int i = 0; i <= n+5; i++)
            par[i] = i;
        num = 0;
        len = 0;
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                cin>>a[i][j];

        for(int i = 1; i <= n; i++)
            for(int j = i + 1; j <= n; j++)
            {
                e[num].x = i;
                e[num].y = j;
                e[num++].w = a[i][j];
            }
        sort(e,e+num,cmp);
        for(int i = 0; i < num; i++)
        {
            if(Find(e[i].x) != Find(e[i].y))
            {
                Merge(e[i].x,e[i].y);
                len += e[i].w;
            }
        }
        cout<<len<<endl;
    }

}
int main()
{
    freopen("input.txt","r",stdin);
    kruskal();

    return 0;
}