HDU 1142 A Walk Through the Forest(最短路+记忆化搜索)
A Walk Through the Forest
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 10172 Accepted Submission(s): 3701
The forest is beautiful, and Jimmy wants to take a different route everyday. He also wants to get home before dark, so he always takes a path to make progress towards his house. He considers taking a path from A to B to be progress if there exists a route from B to his home that is shorter than any possible route from A. Calculate how many different routes through the forest Jimmy might take.
1 3 2
1 4 2
3 4 3
1 5 12
4 2 34
5 2 24
7 8
1 3 1
1 4 1
3 7 1
7 4 1
7 5 1
6 7 1
5 2 1
6 2 1
0
4
#include<iostream>
#include<stdio.h>
#include<memory.h>
using namespace std;
#define max_v 1005
#define INF 9999999
int n,m;
int vis[max_v];
int dis[max_v];
int e[max_v][max_v];
int dp[max_v];
void init()
{
memset(vis,,sizeof(vis));
for(int i=;i<=n;i++)
{
for(int j=;j<=n;j++)
{
e[i][j]=INF;
}
dp[i]=-;
dis[i]=INF;
}
}
void Dijkstra(int s)
{
for(int i=;i<=n;i++)
dis[i]=e[s][i];
dis[s]=;
for(int i=;i<=n;i++)
{
int index,mindis=INF;
for(int j=;j<=n;j++)
{
if(!vis[j]&&dis[j]<mindis)
{
mindis=dis[j];
index=j;
}
}
vis[index]=;
for(int j=;j<=n;j++)
if(dis[index]+e[index][j]<dis[j])
dis[j]=dis[index]+e[index][j];
}
}
int dfs(int v)
{
if(dp[v]!=-)
return dp[v];
if(v==)
return ;
int sum=;
for(int i=;i<=n;i++)
if(dis[v]>dis[i]&&e[v][i]!=INF)
sum+=dfs(i);
dp[v]=sum;
return dp[v];
}
int main()
{
while(~scanf("%d",&n))
{
if(!n)
break;
scanf("%d",&m);
init();
for(int i=;i<m;i++)
{
int x,y,z;
scanf("%d %d %d",&x,&y,&z);
if(e[x][y]>z)
e[x][y]=e[y][x]=z;
}
Dijkstra();
printf("%d\n",dfs());
}
return ;
}
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