Target sum problem

answers.txt

```
 231552 - yes
 234756 - no
 596873 - yes
 648219 - yes
 726312 - yes
 981237 - no
 988331 - yes
1277361 - no
1283379 - no
```

target_sum.py

"""
Usage:

    $ python target_sum.py 231552
    yes
"""

import sys

target = int(sys.argv[1])

# http://stackoverflow.com/questions/2701173/most-efficient-way-for-a-lookup-search-in-a-huge-list-python
# http://wiki.python.org/moin/TimeComplexity
# if memory usage is critical one should use sorted list with bisect from standard library instead of a set 
pairs = set()

for i in open('input.txt'):
    n = int(i)
    if (target - n) in pairs:
        print 'yes'
        sys.exit(0)
    pairs.add(n)

print 'no'