UVA 1395 - Slim Span

题目链接

题意：给定一些结点和边，要求出最苗条度最小的生成树，苗条度定义为：生成树中最大权的边减去最小权的边的值

思路：类似建最小生成树的算法，多一步枚举起始边即可

代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 105;
const int INF = 0x3f3f3f3f;
int n, m, parent[N];

struct Edge {
	int u, v, val;
	Edge() {}
	Edge(int u, int v, int val) {
		this->u = u;
		this->v = v;
		this->val= val;
	}
	void read() {
		scanf("%d%d%d", &u, &v, &val);
	}
} e[N * N];

int find(int x) {
	return x == parent[x] ? x : parent[x] = find(parent[x]);
}

bool cmp(Edge a, Edge b) {
	return a.val < b.val;
}

int main() {
	while (~scanf("%d%d", &n, &m) && n || m) {
		for (int i = 0; i < m; i++)
			e[i].read();
		sort(e, e + m, cmp);
		int ans = INF;
		for (int i = 0; i < m; i++) {
			int cnt = 1;
			for (int j = 1; j <= n; j++) parent[j] = j;
			int flag = 1;
			for (int j = i; j < m; j++) {
				int u = find(e[j].u);
				int v = find(e[j].v);
				if (u != v) {
					parent[u] = v;
					cnt++;
				}
				if (cnt == n) {
					ans = min(ans, e[j].val - e[i].val);
					flag = 0;
					break;
				}
			}
			if (flag) break;
		}
		if (ans == INF) ans = -1;
		printf("%d\n", ans);
	}
	return 0;
}