HDU 1142 A Walk Through the Forest (记忆化搜索 最短路)
A Walk Through the Forest
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 4383 Accepted Submission(s): 1573
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
// File Name: A Walk Through the Forest 1142.cpp
// Author: sheng
// Created Time: 2013年07月18日 星期四 19时57分53秒 #include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std; #ifdef WINDOWS
#define LL __int64
#define LLD "%I64d"
#else
#define LL long long
#define LLD "%lld"
#endif const int max_n = ;
const LL INF = 0x3fffffff;
int n, m;
struct point
{
int x, y;
}; int map[max_n][max_n];
LL vis[max_n], dis[max_n];
LL s[max_n]; LL DFS(int p)
{
s[] = ;
if (s[p] > )
return s[p]; //记忆化
for (int i = ; i <= n; i ++)
{
if ((dis[i] < dis[p]) && map[p][i] < INF)
s[p] += DFS(i); }
return s[p];
} int main ()
{
while (~scanf ("%d", &n) && n)
{
scanf ("%d", &m);
for (int i = ; i <= n; i ++)
for (int j = ; j <= n; j ++)
map[i][j] = INF;
for (int i = ; i < m; i++)
{
int a, b, c;
scanf ("%d%d%d", &a, &b, &c);
map[a][b] = map[b][a] = c;
}
memset(vis, , sizeof (vis));
memset(s, , sizeof(s));
for (int i = ; i <= n; i ++)
{
dis[i] = map[][i];
}
vis[] = ;
for (int i = ; i < n; i ++)
{
int k;
LL min = INF;
for (int j = ; j <= n; j ++)
{
if (!vis[j] && min > dis[j])
{
min = dis[j];
k = j;
}
}
vis[k] = ;
for (int j = ; j <= n; j ++)
{
if (!vis[j] && dis[j] > dis[k] + map[k][j])
dis[j] = dis[k] + map[k][j];
}
}
dis[] = ; //因为从2到2是距离为0的
DFS();
printf (LLD"\n", s[]);
}
return ;
}
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