forked from algorhythms/HackerRankAlgorithms
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Even Tree.py
70 lines (56 loc) · 1.83 KB
/
Even Tree.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
"""
Problem Statement
You are given a tree (a simple connected graph with no cycles). You have to remove as many edges from the tree as
possible to obtain a forest with the condition that : Each connected component of the forest should contain an even
number of vertices.
"""
__author__ = 'Danyang'
class Solution(object):
def __init__(self, N, M):
self.f = [0 for _ in xrange(N + 1)] # store the number of nodes of a subtree rooted at i
self.V = [[] for _ in xrange(N + 1)] # 0 is dummy
self.E = []
def solve(self, cipher):
"""
count the number of subtree with even size
if a subtree is even, it can be detached from else and maintain the else's even odd Parity
:param cipher: the cipher
"""
N, M, E = cipher
for e in E:
u, v = e
self.E.append([u, v])
self.V[u].append(v)
self.V[v].append(u)
self.get_sum(1, 0)
result = 0
for i in xrange(2, N + 1): # excluding root
if self.f[i] % 2 == 0:
result += 1
return result
def get_sum(self, cur, pi):
"""
reduce graph to tree
dp (graph is mostly top-down dp)
dfs
"""
if self.f[cur] == 0:
for nigh in self.V[cur]:
if nigh != pi:
self.f[cur] += self.get_sum(nigh, cur) # child
self.f[cur] += 1 # itself
return self.f[cur]
if __name__ == "__main__":
import sys
f = open("1.in", "r")
# f = sys.stdin
N, M = map(int, f.readline().strip().split(' '))
solution = Solution(N, M)
E = []
for t in xrange(M):
# construct cipher
E.append(map(int, f.readline().strip().split(' ')))
# solve
cipher = N, M, E
s = "%s\n" % (solution.solve(cipher))
print s,