poj2377 Bad Cowtractors

思路：

最大生成树。

实现：

 #include <iostream>
 #include <cstdio>
 #include <vector>
 #include <algorithm>
 #include <cmath>
 using namespace std;

 struct edge
 {
     int a, b, cost;
 };
 edge es[];
 int ran[];
 int par[];
 int n, m, x, y, c;

 void init(int n)
 {
     for (int i = ; i < n; i++)
     {
         par[i] = i;
         ran[i] = ;
     }
 }

 int find(int x)
 {
     if (par[x] == x)
         return x;
     return par[x] = find(par[x]);
 }

 void unite(int x, int y)
 {
     x = find(x);
     y = find(y);
     if (x == y)
         return;
     if (ran[x] < ran[y])
     {
         par[x] = y;
     }
     else
     {
         par[y] = x;
         if (ran[x] == ran[y])
         {
             ran[x] ++;
         }
     }
 }

 bool same(int x, int y)
 {
     return find(x) == find(y);
 }

 bool cmp(const edge & a, const edge & b)
 {
     return a.cost > b.cost;
 }

 int kru()
 {
     init(n);
     sort(es, es + m, cmp);
     int res = , cnt = ;
     for (int i = ; i < m; i++)
     {
         if (!same(es[i].a, es[i].b))
         {
             unite(es[i].a, es[i].b);
             cnt += ;
             res += es[i].cost;
         }
     }
     return cnt < n -  ? - : res;
 }

 int main()
 {
     scanf("%d %d", &n, &m);
     for (int i = ; i < m; i++)
     {
         scanf("%d %d %d", &x, &y, &c);
         es[i].a = x;
         es[i].b = y;
         es[i].cost = c;
     }
     int tmp = kru();
     printf("%d\n", tmp);
     return ;
 }