使用优先队列+邻接表的prime算法果然比以前的O(n^3)要快很多哈
#include <iostream>
#include <queue>
using namespace std;
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typedef struct
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{
long v;
long next;
long cost;
}Edge;
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typedef struct
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![](https://www.cnblogs.com/Images/OutliningIndicators/ContractedBlock.gif)
{
long v;
long cost;
}node;
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bool operator <(const node &a,const node &b)
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{
return a.cost>b.cost;
}
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priority_queue<node> q;
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const long MAXN=10000;
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Edge e[MAXN];
long p[MAXN];
bool vist[MAXN];
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long m,n;
long from,to,cost;
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void init()
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{
memset(p,-1,sizeof(p));
memset(vist,0,sizeof(vist));
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while (!q.empty())
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{
q.pop();
}
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long i;
long eid=0;
for (i=0;i<n;++i)
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{
scanf("%ld %ld %ld",&from,&to,&cost);
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e[eid].next=p[from];
e[eid].v=to;
e[eid].cost=cost;
p[from]=eid++;
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//以下适用于无向图
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swap(from,to);
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e[eid].next=p[from];
e[eid].v=to;
e[eid].cost=cost;
p[from]=eid++;
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}
}
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void print(long cost)
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{
printf("%ld\n",cost);
}
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void Prime()
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{
long cost=0;
init();
node t;
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t.v=from;//选择起点
t.cost=0;
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q.push(t);
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long tt=0;
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while (!q.empty()&&tt<m)
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{
t=q.top();
q.pop();
if (vist[t.v])
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{
continue;
}
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cost+=t.cost;
++tt;
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vist[t.v]=true;
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long j;
for (j=p[t.v];j!=-1;j=e[j].next)
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{
if (!vist[e[j].v])
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{
node temp;
temp.v=e[j].v;
temp.cost=e[j].cost;
q.push(temp);
}
}
}
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print(cost);
}
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int main()
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{
while (scanf("%ld %ld",&m,&n)!=EOF)
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{
Prime();
}
return 0;
}