credit.py

#!/usr/bin/env python
import sys

credit = 200
prices = [150, 24, 79, 50, 88, 345, 3]
n = len(prices)

k = 0
sort = sorted(enumerate(prices), key=lambda x:x[1])
r = n - 1
l = 0

while sort[r][1] + sort[l][1] > credit and r > l:
    r -= 1
while sort[r][1] + sort[l][1] < credit and r > l:
    l += 1

print r, l