hdu1142-A Walk Through the Forest-最短路+dfs

下面是spfa+dfs

//56017202012-03-21 20:40:48Accepted114231MS624K1382 BC++zjwzcnjsy#include <cstdio>#include <vector>#include <queue>using namespace std;#define inf 0x3fffffff#define M 1001struct son{    int v,w;    son(int tv,int tw):v(tv),w(tw){}};vector<son>g[M];int n,m;int dist[M],inq[M];__int64 ans[M];;void init(){    for(int i=0;i<=n;++i)g[i].clear(),ans[i]=-1;}void spfa(int u){    int i,v,w;    for(i=1;i<=n;++i)dist[i]=inf,inq[i]=0;    dist[u]=0;    queue<int>Q;    Q.push(u);inq[u]=1;    while(!Q.empty()){        u=Q.front();Q.pop();inq[u]=0;        for(i=0;i<g[u].size();++i){            v=g[u][i].v;w=g[u][i].w;            if(dist[v]>dist[u]+w){                dist[v]=dist[u]+w;                if(!inq[v]){Q.push(v);inq[v]=1;}            }        }    }}__int64 dfs(int i){/*dfs也要优化，不然也会超时*/     if(ans[i]!=-1)return ans[i];    if(i==2)return 1;    ans[i]=0;    for(int j=0;j<g[i].size();++j)    {        if(g[i][j].v!=i && dist[g[i][j].v]<dist[i]){            ans[i]+=dfs(g[i][j].v);        }    }    return ans[i];}int main(){    int a,b,d,i;    while(scanf("%d",&n)!=EOF&&n){        scanf("%d",&m);        init();        for(i=0;i<m;++i){            scanf("%d%d%d",&a,&b,&d);            g[a].push_back(son(b,d));            g[b].push_back(son(a,d));        }        spfa(2);        dfs(1);        printf("%I64d\n",ans[1]);    }    return 0;}

下面是dijkstra+dfs

//56017632012-03-21 20:44:11Accepted114293MS4156K1317 BC++zjwzcnjsy#include <stdio.h>#define inf 0x3fffffff#define M 1001int dist[M],map[M][M],n,m;__int64 ans[M];void init(){    for(int i=1;i<=n;++i){        ans[i]=-1;        for(int j=1;j<=n;++j)map[i][j]=(i==j?0:inf);    }}void dijkstra(int u){    int v[M],i,j,min,w;    for(i=1;i<=n;++i)dist[i]=map[u][i],v[i]=0;    dist[u]=0;v[u]=1;    for(i=0;i<n;i++){        min=inf;        for(j=1;j<=n;++j){            if(!v[j] && dist[j]<min){min=dist[j];w=j;}        }        v[w]=1;        for(j=1;j<=n;++j){            if(!v[j] && dist[j]>dist[w]+map[w][j]){dist[j]=dist[w]+map[w][j];}        }    }}__int64 dfs(int i){/*dfs也要优化，不然也会超时*/     if(ans[i]!=-1)return ans[i];    if(i==2)return 1;    ans[i]=0;    for(int j=1;j<=n;++j)    {        if(i!=j && dist[j]<dist[i] && map[i][j]<inf){            ans[i]+=dfs(j);        }    }    return ans[i];}int main(){    int a,b,d,i;    while(scanf("%d",&n)!=EOF&&n){        scanf("%d",&m);        init();        for(i=0;i<m;++i){            scanf("%d%d%d",&a,&b,&d);            if(map[a][b]>d)map[a][b]=map[b][a]=d;        }        dijkstra(2);        dfs(1);        printf("%I64d\n",ans[1]);    }    return 0;}