最小生成樹指的是在圖上面找到權值最小的一棵樹，並且保證圖上所有的點都在這棵樹上。

解決辦法：Kruskal 算法（貪心思想）

/**
 *  Fuck you.
 *  I love you too.
 */

#include<bits/stdc++.h>
#define lson i<<2
#define rson i<<2|1
#define LS l,mid,lson
#define RS mid+1,r,rson
#define mem(a,x) memset(a,x,sizeof(a))
#define gcd(a,b) __gcd(a,b)
#define ll long long
#define ull unsigned long long
#define lowbit(x) (x&-x)
#define enld endl
#define mian main
#define itn int
#define prinft printf

const double PI = acos (-1.0);
const int INF = 0x3f3f3f3f;
const int EXP = 1e-8;
const int N = 1e5 + 5;
const int MOD = 1e9 + 7;
const int MAXN = 1e5 + 5;

using namespace std;

int n;
int ans;
int par[N];

struct ed {
    int s, e, cost;
} edge[MAXN];

bool cmp (ed a, ed b) {
    return a.cost < b.cost;
}

int Find (int a) {
    return a == par[a] ? a : par[a] = Find (par[a]);
}

void join (int a, int b) {
    par[Find (a)] = Find (b);
}

int main() {
    while (~scanf ("%d", &n)) {
        ans = 0;
        for (int i = 0; i < n; ++i) {
            scanf ("%d%d%d", &edge[i].s, &edge[i].e, &edge[i].cost);
            par[edge[i].s] = edge[i].s;
            par[edge[i].e] = edge[i].e;
        }
        sort (edge, edge + n, cmp);
        for (int i = 0; i < n; ++i) {
            if (Find (edge[i].s) != Find (edge[i].e)) {
                cout << edge[i].s << ‘ ‘ << edge[i].e << endl;
                join (edge[i].s, edge[i].e);
                ans += edge[i].cost;
            }
        }
        cout << ans << endl;
    }
    return 0;
}

Kruskal 模板（Hdu - 1162）