poj2387- Til the Cows Come Home

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题目大意：有N个点，给出从a点到b点的距离，当然a和b是互相可以抵达的，问从1到n的最短距离

解题思路：模版题，这题要注意的是有重边，dijkstra的算法需要考虑下，bellman-ford和spfa可以忽略这个问题

 

/*
dijkstra
Memory 4108K
Time   125MS
*/
#include <iostream>
using namespace std;
#define inf 1<<29
#define MAXV 1005

int map[MAXV][MAXV];
int n,m;

void dijkstra(){
	int i,j,min,v;
	int d[MAXV];
	bool vis[MAXV];

	for(i=1;i<=n;i++){
		vis[i]=0;
		d[i]=map[1][i];
	}

	for(i=1;i<=n;i++){
		min=inf;
		for(j=1;j<=n;j++)
			if(!vis[j] && d[j]<min){
				v=j;
				min=d[j];
			}
		vis[v]=1;

		for(j=1;j<=n;j++)
			if(!vis[j] && d[j]>map[v][j]+d[v])
				d[j]=map[v][j]+d[v];
	}
	printf("%d\n",d[n]);
}

int main(){
	int i,j,a,b,c;
	while(~scanf("%d%d",&m,&n)){
		for(i=1;i<=n;i++)
			for(j=1;j<=n;j++)
				if(i==j)
					map[i][i]=0;
				else map[i][j]=map[j][i]=inf;
		
		for(i=1;i<=m;i++){
			scanf("%d%d%d",&a,&b,&c);
			if(map[a][b]>c) map[a][b]=map[b][a]=c;
		}
		dijkstra();
	}
	return 0;
}

=====================================================================================

/*
Memory 188K
Time   16MS
其实bellman-ford在某些时候还是很快滴
*/
#include <iostream>
using namespace std;
#define inf 1<<29
#define MAXM 2005
#define MAXV 1005

typedef struct{
	int a,b,w;
}Edge;

Edge edge[MAXM];
int n,m;

void bellman_ford(){
	int i,j;
	int d[MAXV];
	for(i=2;i<=n;i++) d[i]=inf;
	d[1]=0;

	for(i=1;i<=n;i++){
		for(j=1;j<=m;j++){
			if(d[edge[j].a]>edge[j].w+d[edge[j].b]) d[edge[j].a]=edge[j].w+d[edge[j].b];
			if(d[edge[j].b]>edge[j].w+d[edge[j].a]) d[edge[j].b]=edge[j].w+d[edge[j].a];
		}
	}
	printf("%d\n",d[n]);
}

int main(){
	int i,a,b,c;
	while(~scanf("%d%d",&m,&n)){
		for(i=1;i<=m;i++){
			scanf("%d%d%d",&a,&b,&c);
			edge[i].a=a;
			edge[i].b=b;
			edge[i].w=c;
		}
		bellman_ford();
	}
	return 0;
}

==========================================================================================

 

/*
spfa
Memory 256K
Time   32MS
*/
#include <iostream>
#include <queue>
using namespace std;
#define inf 1<<29
#define MAXM 4005
#define MAXV 1005

typedef struct{
	int a,b,w,next;
}Edge;

Edge edge[MAXM];
int n,m,headlist[MAXV];

void spfa(){
	int i,d[MAXV],v,vis[MAXV];
	queue <int>q;
	for(i=2;i<=n;i++){
		d[i]=inf;
		vis[i]=0;
	}
	d[1]=0;
	vis[1]=1;
	q.push(1);
	while(!q.empty()){
		v=q.front();q.pop();
		vis[v]=0;

		for(i=headlist[v];i!=-1;i=edge[i].next)
			if(d[v]+edge[i].w<d[edge[i].b]){
				d[edge[i].b]=d[v]+edge[i].w;
				if(!vis[edge[i].b]){
					vis[edge[i].b]=1;
					q.push(edge[i].b);
				}
			}
	}
	printf("%d\n",d[n]);
}

int main(){
	int i,a,b,c;
	while(~scanf("%d%d",&m,&n)){
		for(i=1;i<=n;i++) headlist[i]=-1;
		for(i=1;i<=2*m;i+=2){
			scanf("%d%d%d",&a,&b,&c);
			edge[i].a=a;
			edge[i].b=b;
			edge[i].w=c;
			edge[i].next=headlist[a];
			headlist[a]=i;
			edge[i+1].a=b;
			edge[i+1].b=a;
			edge[i+1].w=c;
			edge[i+1].next=headlist[b];
			headlist[b]=i+1;
		}
		spfa();
	}
	return 0;
}