Even Tree

 1 def search(a,b): # 根据核心算法和题目要求要筛选边
 2     seen = {}
 3     seen[a] = True
 4     q = []
 5 
 6     for x in adj[a]:
 7         if x != b:
 8             seen[x] = True
 9             q.append(x)
10     s = len(q) + 1
11     while q:
12         n = q.pop()
13         for x in adj[n]:
14             if x not in seen:
15                 seen[x] = True
16                 q.append(x)
17                 s += 1
18     return (s+1)%2
19 
20 [N,M] = [int(x) for x in raw_input().split(‘ ‘)]
21 edges = [] # 保存边的list
22 adj = {} # 保存邻接的dict
23 for a in xrange(1,N+1): # 初始化
24     adj[a] = []
25 
26 for a in xrange(M):
27     [x,y] = [int(z) for z in raw_input().split(‘ ‘)]
28     adj[x].append(y) # 保存边的对应，没有方向性
29     adj[y].append(x)
30     edges.append((x,y)) # 保存边边
31 
32 count = 0
33 for e in edges:
34     (x,y) = e
35     if search(x,y): #依次查看每个边是否能移开
36         count += 1
37         adj[x].remove(y)
38         adj[y].remove(x)
39 
40 print count