- #1

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## Homework Statement

Given a list of integers and a single sum value, return the first two values (parse from the left please) in order of appearance that add up to form the sum.

Python:

```
sum_pairs([11, 3, 7, 5], 10)
# ^--^ 3 + 7 = 10
== [3, 7]
sum_pairs([4, 3, 2, 3, 4], 6)
# ^-----^ 4 + 2 = 6, indices: 0, 2 *
# ^-----^ 3 + 3 = 6, indices: 1, 3
# ^-----^ 2 + 4 = 6, indices: 2, 4
# * entire pair is earlier, and therefore is the correct answer
== [4, 2]
sum_pairs([0, 0, -2, 3], 2)
# there are no pairs of values that can be added to produce 2.
== None/nil/undefined (Based on the language)
sum_pairs([10, 5, 2, 3, 7, 5], 10)
# ^-----------^ 5 + 5 = 10, indices: 1, 5
# ^--^ 3 + 7 = 10, indices: 3, 4 *
# * entire pair is earlier, and therefore is the correct answer
== [3, 7]
```

**NOTE:**There will also be lists tested of lengths upwards of 10,000,000 elements. Be sure your code doesn't time out.

This is a problem off of codewars.com. I have made two versions that satisfy the eight examples but there is a 12000ms time restraint that I need to overcome. I am not versed in CS so I don't know much about algorithms or how to optimize them.

2. Homework Equations

2. Homework Equations

The examples are:

Python:

```
l1= [1, 4, 8, 7, 3, 15]
l2= [1, -2, 3, 0, -6, 1]
l3= [20, -13, 40]
l4= [1, 2, 3, 4, 1, 0]
l5= [10, 5, 2, 3, 7, 5]
l6= [4, -2, 3, 3, 4]
l7= [0, 2, 0]
l8= [5, 9, 13, -3]
print(sum_pairs(l1, 8) == [1, 7]) #"Basic: %s should return [1, 7] for sum = 8" % l1)
print(sum_pairs(l2, -6) == [0, -6]) #"Negatives: %s should return [0, -6] for sum = -6" % l2)
print(sum_pairs(l3, -7) == None) #"No Match: %s should return None for sum = -7" % l3)
print(sum_pairs(l4, 2) == [1, 1]) #"First Match From Left: %s should return [1, 1] for sum = 2 " % l4)
print(sum_pairs(l5, 10) == [3, 7]) #"First Match From Left REDUX!: %s should return [3, 7] for sum = 10 " % l5)
print(sum_pairs(l6, 8) == [4, 4]) #"Duplicates: %s should return [4, 4] for sum = 8" % l6)
print(sum_pairs(l7, 0) == [0, 0]) #"Zeroes: %s should return [0, 0] for sum = 0" % l7)
print(sum_pairs(l8, 10) == [13, -3]) #"Subtraction: %s should return [13, -3] for sum = 10" % l8)
```

They should all return True

## The Attempt at a Solution

My first attempt is simple and straight forward:

Python:

```
def sum_pairs(ints, s):
prev_list = []
for num in ints:
for test in prev_list:
if num+test == s:
return ([test, num])
prev_list += [num]
```

Python:

```
def sum_pairs(ints, s):
neg_list = []
pos_list = []
for num in ints:
if num > s:
for neg in neg_list:
if neg == s - num:
return [neg,num]
else:
for pos in pos_list:
if pos == s - num:
return [pos,num]
if num < 0:
neg_list += [num]
else:
pos_list += [num]
```

From here, my plan was to make four lists: two negatives with one where abs(number) >= abs(s) and the other abs(number) < abs(s) with a similar pattern for positive numbers. I think it might be helpful to find the sign of 's' at the very beginning but I haven't figured out how to use that to my advantage..

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