poj2253 Dijkstra变形

最新推荐文章于 2019-01-20 21:02:37 发布

小狐狸jun

最新推荐文章于 2019-01-20 21:02:37 发布

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分类专栏： ACM 图论文章标签： dijkstra Dijkstra

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在一片宁静的湖面上，Freddy 蛙正坐在一块石头上，突然注意到另一块石头上的 Fiona 蛙。他计划拜访她，但因水中有游客的防晒霜而不想游泳。为避免这一麻烦，Freddy 考虑通过跳跃来到达 Fiona 的石头。然而，由于距离过远，他需要借助其他石头作为中转站，进行一系列小跳跃。此挑战在于计算青蛙之间的最短跳跃距离，即“青蛙距离”，并确保每一步跳跃范围足够覆盖所涉及的距离。

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Description

Freddy Frog is sitting on a stone in the middle of a lake. Suddenly he notices Fiona Frog who is sitting on another stone. He plans to visit her, but since the water is dirty and full of tourists' sunscreen, he wants to avoid swimming and instead reach her by jumping.
Unfortunately Fiona's stone is out of his jump range. Therefore Freddy considers to use other stones as intermediate stops and reach her by a sequence of several small jumps.
To execute a given sequence of jumps, a frog's jump range obviously must be at least as long as the longest jump occuring in the sequence.
The frog distance (humans also call it minimax distance) between two stones therefore is defined as the minimum necessary jump range over all possible paths between the two stones.

You are given the coordinates of Freddy's stone, Fiona's stone and all other stones in the lake. Your job is to compute the frog distance between Freddy's and Fiona's stone.

Input

The input will contain one or more test cases. The first line of each test case will contain the number of stones n (2<=n<=200). The next n lines each contain two integers xi,yi (0 <= xi,yi <= 1000) representing the coordinates of stone #i. Stone #1 is Freddy's stone, stone #2 is Fiona's stone, the other n-2 stones are unoccupied. There's a blank line following each test case. Input is terminated by a value of zero (0) for n.

Output

For each test case, print a line saying "Scenario #x" and a line saying "Frog Distance = y" where x is replaced by the test case number (they are numbered from 1) and y is replaced by the appropriate real number, printed to three decimals. Put a blank line after each test case, even after the last one.

Sample Input

Sample Output

Scenario #1
Frog Distance = 5.000

Scenario #2
Frog Distance = 1.414

做题都做蒙了。但这题让我很好的了解变形，运用一种算法时，根据具体题目变形。。。

dis[j]代表的是到j点的答案。。。。。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define N 210
#define maxt 1010
using namespace std;
int n,Nn;
double map[N][N];
double dis[N];
int vis[N];
double x[N],y[N];
double dist(double x,double y,double x1,double y1)
{
    return sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));
}
double max(double a,double b)
{
	return a>b?a:b;
}
void Dijkstra(int start)
{
    double minimum,min;
    int k,j,i;
    memset(vis,0,sizeof(vis));
    for(i=1;i<=n;i++)
        dis[i]=map[start][i];
    vis[start]=true;

    minimum=0;
    for(i=1;i<n;i++)
    {
        min=maxt;
        for(j=1;j<=n;j++)
        if(dis[j]<min&&!vis[j])
            {
                min=dis[j];
                k=j;
            }
    if(i==1)
        minimum=min;

    vis[k]=true;
    if(k==2)
    {
        cout<<"Scenario #"<<Nn<<endl;
        cout<<"Frog Distance = ";
        printf("%.3f\n\n",dis[2]);
        break;
    }
    for(j=1;j<=n;j++)
    if(dis[j]>max(dis[k],map[k][j])&&!vis[j])
        {
            dis[j]=max(dis[k],map[k][j]);
        }
    }
}
int main()
{
    int i,j;
    Nn=0;
    while(cin>>n,n)
    {
        for(i=1;i<=n;i++)
            cin>>x[i]>>y[i];

        for(i=1;i<=n;i++)
        for(j=1;j<=n;j++)
            map[i][j]=maxt;

        for(i=1;i<=n;i++)
        for(j=1;j<=n;j++)
            {
                map[i][j]=dist(x[i],y[i],x[j],y[j]);
                map[j][i]=map[i][j];
            }
            Nn++;
        Dijkstra(1);
    }
    return 0;
}