Think:
1知識點：最小生成樹Kruskal演算法（並查集思想）
2反思：注意變數初始化

以下為Accepted程式碼

#include <bits/stdc++.h>

using namespace std;

struct node {
    int u;
    int v;
    int w;
}e[1004];

int n, f[1004];

void Init();
int get_f(int v);
bool Merge(int u, int v);

bool cmp(struct node a, struct node b){
    return
 
 (a.w < b.w);
}

int main(){
    int m, i, cnt, sum;
    while(scanf("%d %d", &n, &m) != EOF){
        Init();
        for(i = 1; i <= m; i++){
            scanf("%d %d %d", &e[i].u, &e[i].v, &e[i].w);
        }
        sort(e+1, e+m+1, cmp);
        cnt = 0, sum = 0;///初始化
        for
 
(i = 1; i <= m; i++){
            if(cnt == n-1)
                break;
            if(!Merge(e[i].u, e[i].v)){
                sum += e[i].w;
                cnt++;
            }
        }
        if(cnt == n-1){
            printf("%d\n", sum);
        }
        else {
            printf("-1\n"
 
);
        }
    }
    return 0;
}
void Init(){
    for(int i = 1; i <= n; i++)
        f[i] = i;
}
int get_f(int v){
    if(f[v] == v)
        return f[v];
    else {
        f[v] = get_f(f[v]);
        return f[v];
    }
}
bool Merge(int u, int v){
    int t1 = get_f(u);
    int t2 = get_f(v);
    if(t1 == t2){
        return true;
    }
    else {
        f[t2] = t1;
        return false;
    }
}


/***************************************************
User name: 
Result: Accepted
Take time: 0ms
Take Memory: 236KB
Submit time: 2017-07-14 09:44:16
****************************************************/