HDU 1863 畅通工程

/*
简单最小生成树问题
*/
#include <cstdio>
#include <cstring>
#include <cstdlib>
const int mMax = 107;
const int nMax = 10007;
int N, M;
int u[nMax], v[nMax], w[nMax], r[nMax];
int p[mMax];
int cmp(const void *a, const void *b)
{
	int *pa = (int *)a;
	int *pb = (int *)b;
	return w[r[*pa]] - w[r[*pb]];
}
int find(int x)
{
	return p[x] == x ? x : p[x] = find(p[x]);
}
int main()
{
	//freopen("f://data.in", "r", stdin);
	while(scanf("%d %d", &N, &M) != EOF)
	{
		if(!N) break;
		int ans = 0;
		int i;
		for(i = 0; i < N; ++ i)
			scanf("%d %d %d", &u[i], &v[i], &w[i]);
		for(i = 0; i < N; ++ i) r[i] = i;
		for(i = 0; i <= M; ++ i) p[i] = i;
		qsort(r, N, sizeof(r[0]), cmp);
		for(i = 0; i < N; ++ i)
		{
			int x = find(u[r[i]]),
				y = find(v[r[i]]);
			if(x != y) 
			{
				p[x] = y;
				ans += w[r[i]];
			}
		}
		//判断图是否全连通
		bool ok = 1;
		for(i = 2; i <= M; ++ i)
			if(find(1) != find(i))
			{
				ok = 0;
				break;
			}
		if(ok)
			printf("%d\n", ans);
		else
			printf("?\n");
	}
	return 0;
}