HDOJ2120 Ice_cream's world I

Ice_cream's world I

Time Limit: 3000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 1830    Accepted Submission(s): 1060


[align=left]Problem Description[/align]
ice_cream's world is a rich country, it has many fertile lands. Today, the queen of ice_cream wants award land to diligent ACMers. So there are some watchtowers are set up, and wall between watchtowers be build, in order to partition
the ice_cream’s world. But how many ACMers at most can be awarded by the queen is a big problem. One wall-surrounded land must be given to only one ACMer and no walls are crossed, if you can help the queen solve this problem, you will be get a land.
 

[align=left]Input[/align]
In the case, first two integers N, M (N<=1000, M<=10000) is represent the number of watchtower and the number of wall. The watchtower numbered from 0 to N-1. Next following M lines, every line contain two integers A, B mean between
A and B has a wall(A and B are distinct). Terminate by end of file.
 

[align=left]Output[/align]
Output the maximum number of ACMers who will be awarded.

One answer one line.
 

[align=left]Sample Input[/align]

8 10
0 1
1 2
1 3
2 4
3 4
0 5
5 6
6 7
3 6
4 7

 

[align=left]Sample Output[/align]

3

 

题目大意：富裕的ice_cream女王 要给ACMers分地，女王的土地中有很多瞭望塔，女王命令下人在瞭望塔 与瞭望塔之间建立笔直的围墙，被围墙圈起来的土地可以用来奖励ACMers，但是女王不知道最多能奖励多少ACMers，请你来帮忙。
这个题目是使用并查集来做的。关于并查集，我推荐两篇比较好的相关博文：
https://segmentfault.com/a/1190000004023326

http://blog.csdn.net/dm_vincent/article/details/7655764

不知道为何我使用的java挂了，而使用C++的时候，同样的方法就AC了
下面给出代码：

#include<cstdio>
int tree[1111],count=0;
int find(int x)
{
int r=x;
while(r!=tree[r])
r=tree[r];
return r;
}

void megre(int a,int b)
{
int fa,fb;
fa=find(a);
fb=find(b);
if(fa!=fb)
tree[fa]=fb;
else
count++;
}

int main()
{
int n,m,a,b,i;
while(scanf("%d%d",&n,&m)!=EOF)
{
count=0;
for(i=0;i<n;i++)
tree[i]=i;
while(m--)
{
scanf("%d%d",&a,&b);
megre(a,b);
}
printf("%d\n",count);
}
return 0;
}

import java.util.Scanner;
//并查集暂时并不是理解的很深刻，这个是WA了，但不知道为何
//如果有知道的朋友，希望能解答一下
public class Main{
private static Scanner scanner;
private static int tree[];
private static int count;
public static void main(String[] args) {
scanner = new Scanner(System.in);
while(scanner.hasNext()){
count = 0;//一定要归零，不然每个例子都会一直加，就WA了
int n = scanner.nextInt();
int m = scanner.nextInt();
tree = new int[1111];
for (int i = 0; i < n; i++) {
tree[i] = i;
}
for (int i = 0; i < m; i++) {
int a = scanner.nextInt();
int b = scanner.nextInt();
connect(a,b);
}
System.out.println(count);
}
}
private static void connect(int a, int b) {
int ca = find(a);
int cb = find(b);
if(ca != cb){
tree[ca] = cb;
}else {//如果围成了一圈，就++
count++;
}
}
private static int find(int a) {
int num = a;
while(num != tree[num]){
num = tree[num];
}
return num;
}
}