#include <bits/stdc++.h>
using namespace std;
const int MAX_EDGE = 100000;
const int MAX_VERTICES = 100;
struct Edge{
	int len, u, v;
} edge[MAX_VERTICES];
int fa[MAX_VERTICES], nv, ne;
bool cmp(Edge a, Edge b){
	return a.len < b.len;
}
int get_ancestor(int x){
	if(fa[x] == x){
		return fa[x];
	}
	return fa[x] = get_ancestor(fa[x]);
}
bool merge(int x, int y){
	int ance_x = get_ancestor(x);
	int ance_y = get_ancestor(y);
	if(ance_x != ance_y){
		fa[ance_x] = ance_y;
		return true;
	}
	return false;
}
void init(){
	for(int i = 0 ; i <= nv ; i++){
		fa[i] = i;
	}
}
int main(){
	cin >> nv >> ne;
	init();
	for(int i = 1 ; i <= ne ; i++){
		cin >> 	edge[i].u >> edge[i].v >> edge[i].len;
	}
	sort(edge + 1, edge + ne + 1, cmp); //abandon the first space in edge array 
	int rest_vertices = nv, weight_sum = 0, sub_cost = -1; //weight_sum : weight on MST, sub_cost : the maximum edge's weight in MST
	for(int i = 1 ; i <= ne && rest_vertices > 1 ; i++){ // the last situation will be rest_vertices == 1 cause there is just one nodes left
		if(merge(edge[i].u, edge[i].v)){
			weight_sum += edge[i].len;
			rest_vertices--;
			if(edge[i].len > sub_cost){
				sub_cost = edge[i].len;
			}
		} 
	}
	cout << "Minimum cost : " << weight_sum << endl;
	cout << "The maximum edge's weight in MST : " << sub_cost << endl;
	return 0;
}
 

上面的程式碼可以直接用到CCF 201703-4地鐵修建，需要改一下引數和去掉輸出提示，程式碼如下：

#include <bits/stdc++.h>
using namespace std;
const int MAX_EDGE =  200050;
const int MAX_VERTICES = 100050;
struct Edge{
	int len, u, v;
} edge[MAX_EDGE];
int fa[MAX_VERTICES], nv, ne;
bool cmp(Edge a, Edge b){
	return a.len < b.len;
}
int get_ancestor(int x){
	if(fa[x] == x){
		return fa[x];
	}
	return fa[x] = get_ancestor(fa[x]);
}
bool same(int x, int y){
	return get_ancestor(x) == get_ancestor(y);
} 
bool merge(int x, int y){
	int ance_x = get_ancestor(x);
	int ance_y = get_ancestor(y);
	if(ance_x != ance_y){
		fa[ance_x] = ance_y;
		return true;
	}
	return false;
}
int main(){
	cin >> nv >> ne;
	for(int i =  1 ; i <= nv ; i++){
		fa[i] = i;
	}
	int sub_cost = 0;
	for(int i = 1 ; i <= ne ; i++){
		cin >> 	edge[i].u >> edge[i].v >> edge[i].len;
		if(edge[i].u == 1 && edge[i].v == nv || edge[i].u == nv && edge[i].v == 1){
			sub_cost = edge[i].len;
		}
	}
	sort(edge + 1, edge + ne + 1, cmp); //abandon the first space in edge array 
	int rest_vertices = nv, weight_sum = 0; //weight_sum : weight on MST, sub_cost : the maximum edge's weight in MST
	for(int i = 1 ; i <= ne && rest_vertices > 1 ; i++){ // the last situation will be rest_vertices == 1 cause there is just one nodes left
		if(same(1,nv)){	
			break;
		}
		else if(merge(edge[i].u, edge[i].v)){
			weight_sum += edge[i].len;
			rest_vertices--;
			sub_cost = edge[i].len;
		} 
	}
	cout << sub_cost;
	return 0;
}
//此題使用最小生成樹的思路去做並沒有問題，但並不是要得到最小生成樹
//而是找到連通起點和最終點之之間的最小路徑中的最大邊 
 

遺憾的是，用克魯斯卡寫出來也是80分，目前還沒有解決

2018/12/9解決掉了，這個是因為邊集陣列開小了，因為開始邊集陣列大小誤開成了edge[MAX_VERTICES]，改成edge[MAX_EDGE]之後再提交就是100分了