A Walk Through the Forest HDU - 1142

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预处理每个点到终点距离 然后记忆化搜索即可

#include <cstdio>
#include <queue>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 0x3f3f3f3f

struct node1
{
int v;
int w;
int next;
};

struct node2
{
bool friend operator < (node2 n1,node2 n2)
{
return n1.w>n2.w;
}
int v;
int w;
};

node1 edge[2000010];
priority_queue <node2> que;
int first[1010],dis[1010],book[1010],dp[1010];
int n,m,num;

void addedge(int u,int v,int w)
{
edge[num].v=v;
edge[num].w=w;
edge[num].next=first[u];
first[u]=num++;
return;
}

void dijkstra()
{
node2 cur,tem;
int i,u,v,w;
while(!que.empty()) que.pop();
memset(dis,0x3f,sizeof(dis));
memset(book,0,sizeof(book));
tem.v=2,tem.w=0;
que.push(tem);
dis[2]=0;
while(!que.empty())
{
cur=que.top();
que.pop();
u=cur.v;
if(book[u]) continue;
book[u]=1;
for(i=first[u];i!=-1;i=edge[i].next)
{
v=edge[i].v,w=edge[i].w;
if(!book[v]&&dis[v]>dis[u]+w)
{
dis[v]=dis[u]+w;
tem.v=v,tem.w=dis[v];
que.push(tem);
}
}
}
return;
}

int dfs(int cur)
{
int i,v,res;
if(cur==2) return 1;
if(dp[cur]!=-1) return dp[cur];
res=0;
for(i=first[cur];i!=-1;i=edge[i].next)
{
v=edge[i].v;
if(dis[v]!=N&&dis[v]<dis[cur])
{
res+=dfs(v);
}
}
dp[cur]=res;
return res;
}

int main()
{
int i,u,v,w;
while(scanf("%d",&n)!=EOF&&n!=0)
{
scanf("%d",&m);
memset(first,-1,sizeof(first));
num=0;
for(i=1;i<=m;i++)
{
scanf("%d%d%d",&u,&v,&w);
addedge(u,v,w);
addedge(v,u,w);
}
dijkstra();
memset(dp,-1,sizeof(dp));
printf("%d\n",dfs(1));
}
return 0;
}