POJ 2075 Tangled in Cables (c++/java)

http://poj.org/problem?id=2075

题目大意：

给你一些人名，然后给你n条连接这些人名所拥有的房子的路，求用最小的代价求连接这些房子的花费是否满足要求。

思路：

昨天20分钟的题，输入不小心写错了- -|||||看世界杯半场休息随便看了下发现了。。。。T T

用map进行下标的映射，然后求MST即可。

c++

#include<cstdio>
#include<string>
#include<map>
#include<algorithm>
#include<iostream>
using namespace std;
const int MAXN = 500;
int fa[MAXN];
struct edge
{
int from, to;
double val;
bool operator < (const edge& x)const
{
return val < x.val;
}
}e[MAXN*MAXN];
map<string, int> m;

int find(int cur)
{
return cur == fa[cur] ? cur : fa[cur] = find(fa[cur]);
}

int main()
{
int len = 0, n;
double a;
cin >> a >> n;
while (n--)
{
string temp;
cin >> temp;
m[temp] = len++;
}
cin >> n;

for (len = 0; len<n; len++)
{
string from, to;
double value;
cin >> from >> to >> value;
e[len].from = m[from];
e[len].to = m[to];
e[len].val = value;
}

for (int i = 0; i<len; i++)
fa[i] = i;
sort(e, e + len);

double ans = 0;
for (int i = 0; i<len; i++)
{
int from = e[i].from;
int to = e[i].to;
int root_x = find(from);
int root_y = find(to);
if (root_x == root_y) continue;

fa[root_x] = root_y;
ans += e[i].val;
}
if (ans >  a)
printf("Not enough cable\n");
else
printf("Need %.1lf miles of cable\n", ans);
return 0;
}

JAVA:

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.util.Arrays;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {

//final 相当于const
public static final int MAXN=500;
//写起来好不习惯
public static int[] fa=new int[MAXN];
public static TreeMap<String, Integer> m=new TreeMap<String, Integer>();
public static edge[] e=new edge[MAXN*MAXN];
public static int find(int cur)
{
//不能这么写？
//return cur == fa[cur] ? cur : fa[cur] = find(fa[cur]);
if(cur==fa[cur])
return cur;
else
return fa[cur] = find(fa[cur]);
}

public static void main(String[] args) {
int len = 0, n;
double a;

Scanner in=new Scanner(System.in);
a=in.nextDouble();
n=in.nextInt();

while((n--)!=0)
{
String temp=in.next();
m.put(temp, new Integer(len++));
}

n=in.nextInt();

double value;
for (len = 0; len<n; len++)
{
String from=in.next();
String to=in.next();
value=in.nextDouble();
e[len]=new edge();
e[len].from = m.get(from);
e[len].to = m.get(to);
e[len].val = value;
}

for (int i = 0; i<len; i++)
fa[i] = i;

//sort
Arrays.sort(e,0,len);
double ans=0;
for(int i=0;i<len;i++)
{
int from = e[i].from;
int to = e[i].to;
int root_x = find(from);
int root_y = find(to);
if (root_x == root_y) continue;

fa[root_x] = root_y;
ans += e[i].val;
}

if (ans >  a)
System.out.print("Not enough cable\n");
else
System.out.printf("Need %.1f miles of cable\n", ans);
//java 是.1f
}

}

class edge implements  Comparable<edge>
{
int from,to;
double val;
public int compareTo(edge x)
{
//double比较错了一次)
BigDecimal data1 = new BigDecimal(this.val);
BigDecimal data2 = new BigDecimal(x.val);

return data1.compareTo(data2) ;
}
}