How to define a recursive function to merge two sorted lists and return a new list with a increasing order in Python?

Question

I want to define a recursive function to merge two sorted lists (these two lists are sorted) and return a new list containing all the values in both argument lists with a incre

Answer 1

Here are some alternatives:

The smarter way to do this is to use merge function from the heapq module:

from heapq import merge
list(merge(a,b))

Test:

>>> a = [1,2,3,4,7,9]
>>> b = [5,6,7,8,12]
>>> [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 12]

And without using recursion:

def combine(a:list, b:list):    
    alist = []
    i,j = 0,0
    while i < len(a) and j < len(b):
        if a[i] < b[j]:
            alist.append(a[i])
            i+=1
        else:
            alist.append(b[j])
            j+=1

    while i < len(a):
        alist.append(a[i])
        i+=1

    while j < len(b):
        alist.append(b[j])
        j+=1

    return alist

Test:

>>> a = [1,2,3,4,7,9]
>>> b = [5,6,7,8,12]
>>> [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 12]