UVA - 1395 - Slim Span（Kruskal算法+枚举）

将边按权值排序后，枚举最小权值的边，

从第一个边开始，直到往后能够构成生成树，并且记录中间出现过的最大权值和最小权值，

最后不断取最小值即可

切记每次枚举前，都要初始化父亲节点

#include<cstdio>
#include<cstring>
#include<cctype>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<sstream>
#include<iterator>
#include<algorithm>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<deque>
#include<queue>
#include<stack>
#include<list>
typedef long long ll;
typedef unsigned long long llu;
const int MAXN = 100 + 10;
const int MAXT = 100000 + 10;
const int INF = 0x7f7f7f7f;
const double pi = acos(-1.0);
const double EPS = 1e-6;
using namespace std;

struct Line{
int be, en, v;
Line() : be(0), en(0), v(0) {}
bool operator < (const Line &b) const{
return v < b.v;
}
}p[MAXT];

int fa[MAXN], n, m;

int find(int v){
return fa[v] = fa[v] == v ? v : find(fa[v]);
}

int init(){
for(int i = 0; i <= n; ++i) fa[i] = i;
}

int main(){
while(scanf("%d%d", &n, &m) == 2 && (n || m)){
for(int i = 0; i < m; ++i) scanf("%d%d%d", &p[i].be, &p[i].en, &p[i].v);
sort(p, p + m);
int ans = INF;
for(int i = 0; i < m; ++i){
int tmp = 0, cnt = n, ma = -1, mi = INF;
init();
for(int j = i; j < m; ++j){
int t1 = find(p[j].be);
int t2 = find(p[j].en);
if(t1 != t2){
fa[t1] = t2;
ma = max(ma, p[j].v);
mi = min(mi, p[j].v);
if(--cnt == 1) break;
}
}
if(cnt == 1) ans = min(ans, ma - mi);
else break;
}
printf("%d\n", ans == INF ? -1 : ans);
}
return 0;
}