Uva 1395 - Slim Span（枚举+最小生成树）

题目链接 https://vjudge.net/problem/UVA-1395

【题意】
给出一个n个结点(n<=100)的图，求苗条度尽量小的生成树

【思路】
把边权从小到大排序，对于一个连续子区间[L,R]，如果能使这n个点联通，那就一定存在一个苗条度不超过W[R]-W[L]的生成树，二重循环枚举即可

#include<bits/stdc++.h>
using namespace std;

const int maxn = 105;
const int maxm = 5050;

int n, m;
int par[maxn];
struct Edge {
    int from, to, dist;
}edges[maxm];

bool cmp(Edge x, Edge y) { return x.dist < y.dist; }
int find(int x) { return par[x] == x ? x : par[x] = find(par[x]); }

int main() {
    while (scanf("%d%d", &n, &m) == 2) {
        if (!n && !m) break;
        for (int i = 0; i < m; ++i) scanf("%d%d%d", &edges[i].from, &edges[i].to, &edges[i].dist);
        sort(edges, edges + m, cmp);
        int ans = -1;
        for (int i = 0; i < m; ++i) {
            for (int x = 0; x <= n; ++x) par[x] = x;
            int num = 0;
            for (int j = i; j < m; ++j) {
                Edge e = edges[j];
                int x = find(e.from);
                int y = find(e.to);
                if (x != y) { 
                    par[x] = y; 
                    ++num; 
                    if (num == n - 1) {
                        if (-1 == ans) ans = edges[j].dist - edges[i].dist;
                        else ans = min(ans, edges[j].dist - edges[i].dist); 
                    }
                }
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}