以LUOGU 3366爲測試例題（POJ掛了我能怎麼辦我也很絕望啊）
Kruskal 按秩並查集 AC
#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 5000 + 10;
const int MAXM = 200000 + 10;
struct node { int u, v, cost; }edge[MAXM];
int n, m, fa[MAXN], rank[MAXN];
inline void init() { for(int i = 1; i <= n; ++i) fa[i] = i, rank[i] = 0; }
inline bool cmp(node a, node b) { return a.cost < b.cost; }
inline int find(int x) { return fa[x] == x ? x : fa[x] = find(fa[x]); }
inline bool same(int a, int b) { return find(a) == find(b); }
inline void unite(int x, int y) {
x = find(x), y = find(y);
if(x == y) return;
if(rank[x] < rank[y]) fa[x] = y;
else {
fa[y] = x;
if(rank[x] == rank[y]) rank[x]++;
}
}
inline int kruskal() {
sort(edge + 1, edge + m + 1, cmp);
init();
int res = 0;
for(int i = 1; i <= m; ++i) {
node e = edge[i];
if(!same(e.u, e.v)) {
unite(e.u, e.v);
res += e.cost;
}
}
return res;
}
int main() {
scanf("%d%d", &n, &m);
for(int i = 1, u, v, w; i <= m; ++i) {
scanf("%d%d%d", &u, &v, &w);
edge[i].u = u; edge[i].v = v; edge[i].cost = w;
}
int ans = kruskal(), tmp = find(1);
bool flag = false;
for(int i = 2; i <= n; ++i) if(find(i) != tmp) {
flag = true; break;
}
if(flag) puts("orz");
else printf("%d\n", ans);
return 0;
}