POJ 2485 Highways (kruskal+prim)

题目让求使所有点都连通的树的最大边最小的那棵树，的最大边。。。有点拗口，就是求哪棵树的最大边最小。。。求出最大边。

可以转换成，求最小生成树的最大边，因为kruskal中每次加到树中的边都是最小的。

另外，在prim算法中，我用到了在《算法艺术与信息学竞赛--算法竞赛入门经典》上看到的方法，用vector数组来表示图，用pair来方便比较，有意者可看204页的详细说明。

kruskal：

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
struct node
{
int from,to,w;
} edge[250000],t;
int p[501];
int cmp(const node a,const node b)
{return a.w<b.w;}
int find(int i)
{return i==p[i]?i:p[i]=find(p[i]);}
int main(void)
{
int cases,n;
int i,j,count;
int from,to,max;

scanf("%d",&cases);
while( cases-- )
{
scanf("%d",&n);
for( i = 1,count = 0; i <= n; i++ )
for( j = 1; j <= n; j++ )
{
t.from = i;
t.to = j;
scanf("%d",&t.w);
if( i == j ) continue;
count++;
edge[count] = t;
}

for( i = 1; i <= n; i++ ) p[i] = i;
sort(edge+1,edge+1+count,cmp);
for( i = 1,max = -1; i <= count; i++ )
{
from = edge[i].from;to = edge[i].to;
from = find(from);to = find(to);
if( from == to ) continue;
p[from] = to;
if( edge[i].w > max )
max = edge[i].w;
}
printf("%d/n",max);
}

return 0;
}

prim：

#include<cstdio>
#include<iostream>
#include<queue>
#include<vector>
using namespace std;
const int INF = 99999999;
typedef pair<int,int> pii;
vector<pii> G[501];
priority_queue< pii,vector<pii>,greater<pii> > q;
int main(void)
{
int cases,n;
int i,j,k;
int max,from,to,w;
int dist[501],flag[501];
scanf("%d",&cases);
while( cases-- )
{
scanf("%d",&n);
for( i = 1; i <= n; i++ )
{
G[i].clear();
dist[i] = INF;
flag[i] = 0;
}
for( i = 1; i <= n; i++ )
for( j = 1; j <= n; j++ )
{
scanf("%d",&w);
if( w == 0 || i == j ) continue;
G[i].push_back(make_pair(w,j));
}
while( !q.empty() ) q.pop();
q.push(make_pair(0,1));
max = -1;dist[1] = 0;
while( !q.empty() )
{
pii u = q.top();q.pop();
to = u.second;
if( flag[to] ) continue;
flag[to] = 1;
w = u.first;
if( w > max ) max = w;
for( i = 0; i < G[to].size(); i++ )
{
pii a = G[to][i];
if( dist[a.second] > a.first )
{
dist[a.second] = a.first;
q.push(G[to][i]);
}
}
}
printf("%d",max);
}
return 0;
}