# Question

- Given two lists, l1 and l2, write a program to create a third list l3 by picking an odd-index element from the list l1 and even index elements from the list l2.

**Given**:

```
l1 = [3, 6, 9, 12, 15, 18, 21]
l2 = [4, 8, 12, 16, 20, 24, 28]
```

**Expected Output**:

```
Element at odd-index positions from list one
[6, 12, 18]
Element at even-index positions from list two
[4, 12, 20, 28]
Printing Final third list
[6, 12, 18, 4, 12, 20, 28]
```

# My solution

- use the list comprehension
- use enumerate() function to generate index and value for each element in each list
- find the remainder of the index divided by two
- if remainder is not zero mean an odd index
- i.e. "if index % 2" is not equal to 0, so it would equal to True

- if the remainder is zero mean an even index
- i.e. if index % 2 is 0, so would equal to false
- list comprehension only accept True condition,
- so "not index % 2" is used

- if remainder is not zero mean an odd index

```
l1 = [3, 6, 9, 12, 15, 18, 21]
l2 = [4, 8, 12, 16, 20, 24, 28]
odd_index_list = [num for index, num in enumerate(l1) if index % 2]
print("Element at odd-index positions from list one")
print(odd_index_list)
even_index_list = [num for index, num in enumerate(l2) if not index % 2]
print("Element at even-index positions from list two")
print(even_index_list)
final_list = odd_index_list + even_index_list
print("Printing Final third list")
print(final_list)
```

# Other solution

- use string slicing method
- for odd elements slice the string from index 1 to the end with a step of 2
- for even elements slice the string form index 0 to the end with a step of 2

```
list1 = [3, 6, 9, 12, 15, 18, 21]
list2 = [4, 8, 12, 16, 20, 24, 28]
res = list()
odd_elements = list1[1::2]
print("Element at odd-index positions from list one")
print(odd_elements)
even_elements = list2[0::2]
print("Element at even-index positions from list two")
print(even_elements)
print("Printing Final third list")
res.extend(odd_elements)
res.extend(even_elements)
print(res)
```

## Credit

exercise on Pynative

## Top comments (0)