POJ 3522 Slim Span

题意：

         求最大边与最小边差值最小的生成树，若不存在生成树则输出-1。

思路：

         用Kruskal算法枚举最小边即可

#include <cstdio>
#include <algorithm>
using namespace std;
const int N = 110, M = 5000;
struct SIDE
{
    int from;
    int to;
    int distance;
}edge[M];
int cnt[N];
bool cmp(const SIDE a, const SIDE b){
    return a.distance < b.distance;
}
int Find(int x){
    return cnt[x] == x ? x : Find(cnt[x]);
}
int main(void)
{
    int n, m, a, b, MIN, ok;
    while(scanf("%d %d", &n, &m), n+m)
    {
        for(int i=0; i<m; ++i)
            scanf("%d %d %d", &edge[i].from, &edge[i].to, &edge[i].distance);
        sort(edge, edge+m, cmp);
        MIN = 0x3f3f3f3f;
        ok = 0;
        for(int start=0; start<=m-n+1; ++start)
        {
            for(int i=1; i<=n; ++i)
                cnt[i] = i;
            int i, j = 0;
            for(i=start; i<m && j<n-1; ++i)
            {
                a = Find(edge[i].from);
                b = Find(edge[i].to);
                if(a != b)
                    cnt[b] = a, ++j;
            }
            if(j == n-1)
                MIN = min(MIN, edge[i-1].distance - edge[start].distance), ok = 1;
        }
        printf("%d
", ok ? MIN : -1);
    }
}