poj2075 Tangled in Cables 最小生成樹+map，kruskal

題目鏈接：http://poj.org/problem?id=2075

思路：最小生成樹問題，只是點集是以字符串的形式給出的，使用一個map建立string到int的映射就好了。還是kruskal算法。kruskal算法用熟了不想試着寫prim了。。。

///2014.7.11
///poj2075

//Accepted    780K    16MS    G++ 1546B   2014-07-11 23:39:33

/*
 *最小生成樹 + map
 */

#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <map>
using namespace std;

int n,m;
double has,need;
struct Vdge
{
    int x,y;
    double l;
};
Vdge vdge[50000];
bool cmp(Vdge a,Vdge b){
    return a.l<b.l;
}
int dSet[300];
int find(int x){
    while( x != dSet[x] )
        x = dSet[x];
    return x;
}
bool judge(int x,int y){
    int fx = find(x);
    int fy = find(y);
    if( fx==fy )
        return false;
    else{
        dSet[fx] = fy;
        return true;
    }
}

void init(){
    map<string,int> name;
    cin>>has>>n;
    string nname;
    for(int i=0 ; i<n ; i++){
        cin>>nname;
        name[nname] = i;
    }
    cin>>m;
    string name1,name2;
    double temp;
    for(int i=0 ; i<m ; i++){
        cin>>name1>>name2>>temp;
        vdge[i].x = name[name1];
        vdge[i].y = name[name2];
        vdge[i].l = temp;
    }
    for(int i=0 ; i<n ; i++)
        dSet[i] = i;
    sort(vdge,vdge+m,cmp);
    need = 0;
}
void kruskal(){
    int i=0,j=0;
    while( i<n-1 ){
        if( judge(vdge[j].x,vdge[j].y) ){
            need += vdge[j].l;
            i++;
        }
        j++;
    }
}

int main(){
    // freopen("in","r",stdin);
    // freopen("out","w",stdout);

    init();
    // out();
    kruskal();
    if( need <= has )
        cout<<"Need "<<need<<" miles of cable"<<endl;
    else
        cout<<"Not enough cable"<<endl;
    return 0;
}