Problem Description

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.

 

Input

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.

 

Output

Output the maximum number of ACMers who will be awarded.

One answer one line.

 

Sample Input

8 10

0 1

1 2

1 3

2 4

3 4

0 5

5 6

6 7

3 6

4 7

 

Sample Output

3

 

题解：并查集查有多少个圈

时间复杂度：$O(m)$

代码：

#include 
       
        using namespace std;int f[10010];int n, m, cnt;void init() {	for(int i = 0; i < 10010; i ++)	f[i] = i;}int Find(int x) {  if(x != f[x]) f[x] = Find(f[x]);  return f[x];}void Merge(int x, int y) {	int fx = Find(x);	int fy = Find(y);	if(fy != fx)        f[fy] = fx;	else        cnt++;}int main() {	while(~scanf("%d%d", &n, &m)) {		init();		int a, b;		cnt = 0;		for(int i = 0; i < m; i ++) {			scanf("%d%d", &a, &b);			Merge(a, b);		}		printf("%d\n", cnt);	}	return 0;}