# How can I merge two lists and sort them according to "linear" time?

I have this, and it works:

``````# E. Given two lists sorted in increasing order, create and return a merged
# list of all the elements in sorted order. You may modify the passed in lists.
# Ideally, the solution should work in "linear" time, making a single
# pass of both lists.
def linear_merge(list1, list2):
finalList = []
for item in list1:
finalList.append(item)
for item in list2:
finalList.append(item)
finalList.sort()
return finalList
return
```
```

But, I'd really like to learn this stuff well. :) What does 'linear' time mean?

Linear means O(n) in Big O notation, while your code uses a `sort()` which is most likely `O(nlogn)`.

The question is asking for the standard merge algorithm. A simple Python implementation would be:

``````def merge(l, m):
result = []
i = j = 0
total = len(l) + len(m)
while len(result) != total:
if len(l) == i:
result += m[j:]
break
elif len(m) == j:
result += l[i:]
break
elif l[i] < m[j]:
result.append(l[i])
i += 1
else:
result.append(m[j])
j += 1
return result

>>> merge([1,2,6,7], [1,3,5,9])
[1, 1, 2, 3, 5, 6, 7, 9]
```
```