poj 2253 dijstra变形

dijstra算法的变形，定义：dist[i]为源点到点i的若干路径上的边的最大值的最小值，然后会发现可以用和dijstra一样的贪心方法，当前dist最小的以后都不会再被更新。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
using namespace std;

const int INF = 9999999;
const int N = 201;
int head[N];
int dist[N];
bool visit[N];
int n, e;

struct Node 
{
    int x, y;
} node[N];

struct Edge 
{
    int v, next, w;
} edge[N * N];

void addEdge( int u, int v, int w )
{
    edge[e].v = v;
    edge[e].w = w;
    edge[e].next = head[u];
    head[u] = e++;
}

int dis( int i, int j )
{
    return ( node[i].x - node[j].x ) * ( node[i].x - node[j].x ) + 
           ( node[i].y - node[j].y ) * ( node[i].y - node[j].y );
}

void dij( int s )
{
    memset( visit, false, sizeof(visit) );
    for ( int i = 0; i <= n; i++ )
    {
        dist[i] = INF;
    }
    dist[s] = 0;
    for ( int i = 1; i <= n; i++ )
    {
        int u = 0;
        for ( int j = 1; j <= n; j++ )
        {
            if ( !visit[j] && dist[j] < dist[u] )
            {
                u = j;
            }
        }
        visit[u] = true;
        for ( int j = head[u]; j != -1; j = edge[j].next )
        {
            int v = edge[j].v, w = edge[j].w;
            if ( visit[v] ) continue;
            dist[v] = min( dist[v], max( dist[u], w ) );
        }
    }
}

int main ()
{
    int _case = 1;
    while ( scanf("%d", &n), n )
    {
        e = 0;
        memset( head, -1, sizeof(head) );
        for ( int i = 1; i <= n; i++ )
        {
            scanf("%d%d", &node[i].x, &node[i].y);
            for ( int j = i - 1; j > 0; j-- )
            {
                int tmp = dis( i, j );
                addEdge( i, j, tmp );
                addEdge( j, i, tmp );
            }
        }
        dij(1);
        double ans = sqrt( dist[2] * 1.0 );
        printf("Scenario #%d
Frog Distance = %.3lf

", _case++, ans);
    }
    return 0;
}