针对此Codejam问题,Python中更快或更高内存的解决方案

The Problem:

You are hosting a party with G guests
and notice that there is an odd number
of guests! When planning the party you
deliberately invited only couples and
gave each couple a unique number C on
their invitation. You would like to
single out whoever came alone by
asking all of the guests for their
invitation numbers.

The Input:

The first line of input gives the number of cases,N.
N test cases follow. For each test case there will be:

• One line containing the value G the
  number of guests.
• One line containing
  a space-separated list of G integers.
  Each integer C indicates the
  invitation code of a guest. Output

For each test case,output one line
containing “Case #x: ” followed by the
number C of the guest who is alone.

The Limits:

• 1 ≤ N ≤ 50
• 0 < C ≤ 2147483647

Small dataset

3 ≤ G < 100

Large dataset

3 ≤ G < 1000

样本输入：

3
3
1 2147483647 2147483647
5
3 4 7 4 3
5
2 10 2 10 5

样本输出：

Case #1: 1
Case #2: 7
Case #3: 5

这是我提出的解决方案：

with open('A-large-practice.in') as f:
    lines = f.readlines()

with open('A-large-practice.out','w') as output:
    N = int(lines[0])
    for testcase,i in enumerate(range(1,2*N,2)):
        G = int(lines[i])
        for guest in range(G):
            codes = map(int,lines[i+1].split(' '))
            alone = (c for c in codes if codes.count(c)==1)
        output.write("Case #%d: %dn" % (testcase+1,alone.next()))

它使用large input在我的机器上运行12秒.

现在,我的问题是,这个解决方案可以在Python中改进,以便在更短的时间内运行或使用更少的内存吗？该问题的analysis提供了一些关于如何在Java和C中执行此操作的指示,但我无法将这些解决方案转换回Python.

编辑：

结合Alex Martelli和IVlad的提示我现在有这个解决方案,运行在0.079s：

with open('A-large-practice.in') as f:
    lines = f.readlines()

with open('A-large-practice.out',2)):
        codes = map(int,lines[i+1].split(' '))
        alone = 0
        for c in codes: alone ^= c
        output.write("Case #%d: %d" % (testcase+1,alone))