Part Acquisition(spfa输出路径)

Part Acquisition

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 4080		Accepted: 1742		Special Judge

Description

The cows have been sent on a mission through space to acquire a new milking machine for their barn. They are flying through a cluster of stars containing N (1 <= N <= 50,000) planets, each with a trading post.

The cows have determined which of K (1 <= K <= 1,000) types of objects (numbered 1..K) each planet in the cluster desires, and which products they have to trade. No planet has developed currency, so they work under the barter system: all trades consist of each party trading exactly one object (presumably of different types).

The cows start from Earth with a canister of high quality hay (item 1), and they desire a new milking machine (item K). Help them find the best way to make a series of trades at the planets in the cluster to get item K. If this task is impossible, output -1.

Input

* Line 1: Two space-separated integers, N and K.

* Lines 2..N+1: Line i+1 contains two space-separated integers, a_i and b_i respectively, that are planet i's trading trading products. The planet will give item b_i in order to receive item a_i.

Output

* Line 1: One more than the minimum number of trades to get the milking machine which is item K (or -1 if the cows cannot obtain item K).

* Lines 2..T+1: The ordered list of the objects that the cows possess in the sequence of trades.

Sample Input

6 5
1 3
3 2
2 3
3 1
2 5
5 4

Sample Output

4
1
3
2
5
题意；母牛想用草换k星奶机；输出路径；bellman只是单纯的找dis的最小值，会陷入2 3,3 2循环
spfa：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
#include<stack>
#include<queue>
using namespace std;
const int INF=0x3f3f3f3f;
const double PI=acos(-1.0);
typedef long long LL;
#define mem(x,y) memset(x,y,sizeof(x))
#define T_T while(T--)
#define F(i,x) for(i=1;i<=x;i++)
#define SI(x) scanf("%d",&x)
#define SL(x) scanf("%lld",&x)
#define PI(x) printf("%d",x)
#define PL(x) printf("%lld",x)
#define P_ printf(" ")
const int MAXN=1010;
const int MAXM=50010;
int vis[MAXN],dis[MAXN],pre[MAXN];
int head[MAXM];
queue<int>S;
int n,k,edgnum;
struct Edge{
	int from,to,next;
}edg[MAXM];
void initial(){
	mem(head,-1);
	edgnum=0;
	mem(pre,0);
}
void add(int u,int v){
	Edge E={u,v,head[u]};
	edg[edgnum]=E;
	head[u]=edgnum++;
}
void print(int x){
	if(x==0)return;
	print(pre[x]);
	printf("%d\n",x);
}
void spfa(int sx){
	while(!S.empty())S.pop();
	mem(vis,0);mem(dis,INF);
	S.push(sx);vis[sx]=1;dis[sx]=1;
	while(!S.empty()){
		int u=S.front();
		vis[u]=0;
		S.pop();
		for(int i=head[u];i!=-1;i=edg[i].next){
			int v=edg[i].to;
			if(dis[v]>dis[u]+1){
				dis[v]=dis[u]+1;
				if(!vis[v]){
					pre[v]=u;
					vis[v]=1;
					S.push(v);
				}
			}
		}
	}
	if(dis[k]==INF){
		puts("-1");
		return;
	}
	printf("%d\n",dis[k]);
	print(k);
	return;
}
int main(){
	  while(~scanf("%d%d",&n,&k)){
	  	initial();
	  	int i,j,u,v;
	  	F(i,n){
	  		scanf("%d%d",&u,&v);
	  		add(u,v);
		  }
		  spfa(1);
	  }
	return 0;
}

bellman死循环：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
using namespace std;
const int INF=0x3f3f3f3f;
const double PI=acos(-1.0);
typedef long long LL;
#define mem(x,y) memset(x,y,sizeof(x))
#define T_T while(T--)
#define F(i,x) for(i=1;i<=x;i++)
#define SI(x) scanf("%d",&x)
#define SL(x) scanf("%lld",&x)
#define PI(x) printf("%d",x)
#define PL(x) printf("%lld",x)
#define P_ printf(" ")
const int MAXN=50010;
struct Node{
	int u,v;
}dt[MAXN<<1];
int dis[MAXN],pre[MAXN];
int edgnum;
int n,k;
void add(int u,int v){
	dt[edgnum].u=u;
	dt[edgnum++].v=v;
}
void print(int x){
	if(pre[x]==0)return;
	print(pre[x]);
	printf("%d\n",x);
}
int Bellman(int u){
	mem(dis,INF);dis[u]=0;
	for(int i=1;i<=k;i++){
		int u,v;
		for(int j=0;j<edgnum;j++){
		//	dis[v]=min(dis[v],dis[u]+1);
		if(dis[v]>dis[u]+1){
			dis[v]=dis[u]+1;
			pre[v]=u;
			}
		}
	}
	if(dis[k]==INF)return -1;
	print(k);
	return dis[k];
}
int main(){
	while(~scanf("%d%d",&n,&k)){
		int i,j;
		edgnum=0;
		mem(pre,0);
		F(i,n){
			int u,v;
			scanf("%d%d",&u,&v);
			add(u,v);
		}
		printf("%d\n",Bellman(1));
	}
	return 0;
}

dijkscra；不能输出路径。

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
#include<stack>
#include<queue>
using namespace std;
const int INF=0x3f3f3f3f;
const double PI=acos(-1.0);
typedef long long LL;
#define mem(x,y) memset(x,y,sizeof(x))
#define T_T while(T--)
#define F(i,x) for(i=1;i<=x;i++)
#define SI(x) scanf("%d",&x)
#define SL(x) scanf("%lld",&x)
#define PI(x) printf("%d",x)
#define PL(x) printf("%lld",x)
#define P_ printf(" ")
const int MAXN=1010;
const int MAXM=50010;
int vis[MAXN],dis[MAXN],pre[MAXN];
int mp[MAXN][MAXN];
int n,k,edgnum;
void print(int x){
	if(x==0)return;
	print(pre[x]);
	printf("%d\n",x);
}
void dijkscra(int sx){
	mem(dis,INF);mem(vis,0);
	dis[sx]=1;//vis[sx]=1;
	while(true){
		int t=-1,i;
		F(i,n){
			if(!vis[i]&&(t==-1||dis[i]<dis[t]))t=i;
		}
		if(t==-1)break;
		vis[t]=1;
		F(i,n)dis[i]=min(dis[i],dis[t]+mp[t][i]);
	}
	if(dis[k]==INF){
		puts("-1");return;
	}
	printf("%d\n",dis[k]);
	//print(k);
}
int main(){
	  while(~scanf("%d%d",&n,&k)){
	  	mem(mp,INF);mem(pre,0);
	  	int i,j,u,v;
	  	F(i,n){
	  		scanf("%d%d",&u,&v);
	  		mp[u][v]=1;
		  }
		  dijkscra(1);
	  }
	return 0;
}