图论trainning-part-1 B. A Walk Through the Forest
B. A Walk Through the Forest
64-bit integer IO format: %I64d Java class name: Main
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.
Input
Output
Sample Input
5 6
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
Sample Output
2
4 解题:最短距离+记忆化搜索,找出1到终点2上的所有点,假设A,B两点,如果统计d[A] > D[B]这种路径的条数。
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <climits>
#include <vector>
#include <queue>
#include <cstdlib>
#include <string>
#include <set>
#define LL long long
#define INF 0x3f3f3f
using namespace std;
const int maxn = ;
int mp[maxn][maxn],d[maxn],p[maxn];
int n,m;
bool vis[maxn];
void dij(int src){
int i,j,temp,index;
for(i = ; i <= n; i++)
d[i] = INF;
d[src] = ;
memset(vis,false,sizeof(vis));
for(i = ; i < n; i++){
temp = INF;
for(j = ; j <= n; j++)
if(!vis[j] && d[j] < temp) temp = d[index = j];
vis[index] = true;
for(j = ; j <= n; j++)
if(!vis[j] && d[j] > d[index]+mp[index][j])
d[j] = d[index] + mp[index][j];
}
}
int dfs(int s){
if(p[s]) return p[s];
if(s == ) return ;
int i,sum = ;
for(i = ; i <= n; i++){
if(mp[s][i] < INF && d[s] > d[i]) sum += dfs(i);
}
p[s]+= sum;
return p[s];
}
int main(){
int i,j,u,v,w;
while(scanf("%d",&n),n){
scanf("%d",&m);
for(i = ; i <= n; i++)
for(j = ; j <= n; j++)
mp[i][j] = INF;
for(i = ; i < m; i++){
scanf("%d%d%d",&u,&v,&w);
mp[u][v] = mp[v][u] = w;
}
dij();
memset(p,,sizeof(p));
printf("%d\n",dfs());
}
return ;
}
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