[2016-04-13][POJ][2349][Arctic Network]

• 时间:2016-04-13 23:52:36 星期三

• 题目编号:[2016-04-13][POJ][2349][Arctic Network]

• 题目大意:问最小生成树中,第k大的边是多少

• 分析:直接kruskal,合并到倒数第k条边即可

• 遇到的问题:POJ 输出用 %f 而不是 %lf

#include<cstdio>
#include<set>
#include<cmath>
#include<algorithm>
using namespace std;
const int maxn = 500 + 10;
int fa[maxn];
void ini(int n){
    for(int i = 0 ; i <= n ; ++i)
        fa[i] = i;
}
int fnd(int x){
    return x == fa[x] ? x : fa[x] = fnd(fa[x]);
}
struct Point{
    int x,y;
}pp[maxn];
struct Edge{
    int u,v,c;
    Edge(int a=0,int b=0,int cc=0):u(a),v(b),c(cc){}
    bool operator < (const Edge & a)const{
        return c < a.c;
    }   
}e[maxn * maxn];
int dis(int a,int b){
    return (pp[a].x - pp[b].x)*(pp[a].x - pp[b].x) + (pp[a].y - pp[b].y)*(pp[a].y - pp[b].y);
}
int main(){
    int t;   
    scanf("%d",&t);
    while(t--){
        int s,p;
        scanf("%d%d",&s,&p);
        for(int i = 0 ; i < p;++i){
            scanf("%d%d",&pp[i].x,&pp[i].y);
        }   
        ini(p);
        int cnt = 0;
        for(int i = 0 ; i < p; ++i){
            for(int j = 0; j < p ; ++j){
                e[cnt++] = Edge(i,j,dis(i,j));
            }
        }
        sort(e,e+cnt);
        int k = 0,ans = 0;
        for(int i = 0 ; i < cnt; ++i){
            int f1 = fnd(e[i].u);
            int f2 = fnd(e[i].v);
            if(f1 != f2){           
                fa[f1] = f2;
                ++k;               
                if(k == p - s){
                    ans = e[i].c;
                    break;
                }
            }
            if(k == p - 1)    break;
        }
        printf("%.2f\n",sqrt(double(ans)));
    }
    return 0;
}

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