poj2377

最大生成树，注意边数组开二倍大小。注意不连通输出－1；

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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <queue>
using namespace std;

#define maxn 1005
#define maxm 20005

struct Edge
{
int v, next, w;
Edge(int vv, int nn, int ww) :
v(vv), next(nn), w(ww)
{
}
Edge()
{
}
} edge[maxm * 2];

int head[maxn], count;
bool vis[maxn];
int ans = 0;
int m, n;

bool operator< (const Edge &a, const Edge &b)
{
return a.w < b.w;
}

void addedge(int u, int v, int w)
{
edge[count].next = head[u];
edge[count].v = v;
edge[count].w = w;
head[u] = count;
count++;
}

void input()
{
scanf("%d%d", &n, &m);
for (int i = 0; i < m; i++)
{
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
a--, b--;
addedge(a, b, c);
addedge(b, a, c);
}
}

void prim(int src)
{
priority_queue<Edge> pq;
int pre = 0;
Edge temp;
pq.push(Edge(src, 0, 0));
while (!pq.empty())
{
do
{
temp = pq.top();
pq.pop();
} while (!pq.empty() && vis[temp.v]);
if (vis[temp.v])
return;
vis[temp.v] = true;
pre = temp.v;
ans += temp.w;
for (int i = head[pre]; i != -1; i = edge[i].next)
if (!vis[edge[i].v])
pq.push(edge[i]);
}
}

int main()
{
//freopen("t.txt", "r", stdin);
memset(head, -1, sizeof(head));
memset(vis, 0, sizeof(vis));
count = 0;
input();
prim(0);
bool ok = true;
for (int i = 0; i < n; i++)
if (!vis[i])
{
ok = false;
break;
}
if (ok)
printf("%d\n", ans);
else
printf("%d\n", -1);
return 0;
}