并查集-一笔画优化

package 搜索.并查集;
import java.util.Scanner;


/*
 * 1:使用num算出总的合并次数。
 * 5个点，最少要保证合并5-1次才能保证图连通
 * num<n-1;不连通
 * num+1<n
 * n-num>1
 */
public class 一笔画优化 {
static int[] pre;


public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
while (n-- > 0) {
int p = sc.nextInt();
int q = sc.nextInt();
pre = new int[p + 1];
int arr[] = new int[p + 1];
for (int i = 1; i <= p; i++)
pre[i] = i;
int a, b;
int num = 0;// 优化1
for (int i = 0; i < q; i++) {
a = sc.nextInt();
b = sc.nextInt();
arr[a]++;
arr[b]++;
int x = find(a);
int y = find(b);
if (x != y) {
pre[x] = y;
num++;
}
}


if (p - num > 1)
System.out.println("No");
else {
num = 0;
for (int i = 1; i <= p; i++) {
if (num > 2)// 优化2
break;
num += (arr[i] % 2);
}
if (num == 0 || num == 2) {
System.out.println("Yes");
} else {
System.out.println("No");
}
}
}
}


private static int find(int a) {//优化3
if (a == pre[a])
return a;
return pre[a] = find(pre[a]);
}


}