poj 2253

dijkstra借鉴

http://blog.youkuaiyun.com/wangjian8006/article/details/7871812

#include<stdio.h>

#include<math.h>
#define N  300
#define inf 999999999
double map[N][N],dis[N];
double max(double a,double b) {
return a>b?a:b;
}
void dijkstra(int s,int t,int n) {
int visit[N],u,i,j;double min;
for(i=1;i<=n;i++) {
visit[i]=0;
dis[i]=map[s][i];
}
visit[i]=1;
for(i=1;i<n;i++) {
min=inf;
for(j=1;j<=n;j++)
if(min>dis[j]&&visit[j]==0) {
min=dis[j];
u=j;
}
visit[u]=1;
if(u==2)
return ;
for(j=1;j<=n;j++)
if(visit[j]==0&&map[u][j]<dis[j]&&dis[u]<dis[j]) 
dis[j]=max(map[u][j],dis[u]);
}
}
int main() {
int  n,i,j,count=0;
double a[N],b[N],c;
while(scanf("%d",&n),n) {
for(i=1;i<=n;i++) 
for(j=1;j<=n;j++)
map[i][j]=inf;
for(i=1;i<=n;i++)
scanf("%lf%lf",&a[i],&b[i]);
for(i=1;i<n;i++)
for(j=i+1;j<=n;j++) {
c=(a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j]);
map[i][j]=map[j][i]=sqrt(c);
}
dijkstra(1,2,n);
printf("Scenario #%d\nFrog Distance = %.3f\n\n",++count,dis[2]);
}
return 0;

}

flord借鉴http://blog.youkuaiyun.com/lyy289065406/article/details/6645854

#include<stdio.h>
#include<math.h>
#define N 300
#define inf 999999999
double map[N][N],dis[N],a[N],b[N],c;
int main() {
int n,k,i,j,count=0;
while(scanf("%d",&n),n) {
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
map[i][j]=inf;
for(i=1;i<=n;i++) 
scanf("%lf%lf",&a[i],&b[i]);
for(i=1;i<n;i++)
for(j=i+1;j<=n;j++) {
c=(a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j]);
map[i][j]=map[j][i]=sqrt(c);
}
for(k=1;k<=n;k++) 
for(i=1;i<n;i++)
for(j=i+1;j<=n;j++)
if(map[i][j]>map[i][k]&&map[i][j]>map[k][j]) {
if(map[i][k]>map[k][j])
map[i][j]=map[j][i]=map[i][k];
else
map[i][j]=map[j][i]=map[k][j];
}
printf("Scenario #%d\nFrog Distance = %.3f\n\n",++count,map[1][2]);
}
return 0;
}

并查集

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define N 300
int pre[N];
int find(int n ) {
	if(n==pre[n])
		return  n;
return pre[n]=find(pre[n]);
}
struct node {
	int x,y;
	double distance;
}dis[N*N],h;
int cmp(const void *a,const void *b){
	return (*(struct node *)a).distance>(*(struct node *)b).distance?1:-1;
}
int main(){
	int n,m,count=0,i,j,k,f1,f2;
	double c,a[N],b[N];
	while(scanf("%d",&n),n) {
		for(i=1;i<=n;i++)
			pre[i]=i;
		for(i=1;i<=n;i++)
			scanf("%lf%lf",&a[i],&b[i]);
		m=0;
		for(i=1;i<n;i++)
			for(j=i+1;j<=n;j++) {
				c=(a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j]);
				dis[m].x=i;
				dis[m].y=j;
				dis[m++].distance=sqrt(c);
			}
			qsort(dis,m,sizeof(dis[0]),cmp);
			i=0;
			while(find(1)!=find(2)) {
				f1=find(dis[i].x);
			   f2=find(dis[i].y);
			if(f1!=f2)  
				pre[f2]=f1;
			i++;
			}
			printf("Scenario #%d\n",++count);
			printf("Frog Distance = %.3f\n\n",dis[i-1].distance);
			}
			return 0;
	}

二分法http://blog.youkuaiyun.com/aixiaoling1314/article/details/11820271

#include<stdio.h>
#include<math.h>
#define N 300
double map[N][N];
struct node {
int x,y;
}dis[N];
int pre[N],n;
double cmp(int a,int b) {
return sqrt(1.0*(dis[a].x-dis[b].x)*(dis[a].x-dis[b].x)+1.0*(dis[a].y-dis[b].y)*(dis[a].y-dis[b].y));
}
int find(int n) {
if(pre[n]!=n)
pre[n]=find(pre[n]);
return pre[n];
}
int judge(double s) {
int i,j;
for(i=1;i<=n;i++)
pre[i]=i;
for(i=1;i<n;i++)
for(j=i+1;j<=n;j++)
if(map[i][j]<s)
pre[find(i)]=find(j);
if(find(1)==find(2))
return 1;
return 0;
}
int main() {
int t,i,j,m,count=0;
double left,right,mid;
while(scanf("%d",&n),n) {
for(i=1;i<=n;i++)
scanf("%d%d",&dis[i].x,&dis[i].y);
for(i=1;i<n;i++)
for(j=i+1;j<=n;j++)
map[i][j]=cmp(i,j);
left=0;right=map[1][2];
while(right-left>1e-6) {
mid=(left+right)/2;
if(judge(mid))right=mid;
else  left=mid;
}
printf("Scenario #%d\n",++count);
printf("Frog Distance = %.3f\n\n",left);
}
return 0;
}