# Python | Alternate front – rear Sum

While working with python, we usually come by many problems that we need to solve in day-day and in development. Specially in development, small tasks of python are desired to be performed in just one line. We discuss some ways to compute a list consisting of elements that are alternate front-rear sum in the list.

Method #1 : Using loop
This is brute force method in which this problem can be solved. In this, we take two pointers and store their sum in array while increasing and decreasing their positions.

 `# Python3 code to demonstrate  ` `# Alternate front - rear Sum ` `# using loop ` ` `  `# initializing list  ` `test_list ``=` `[``1``, ``4``, ``5``, ``3``, ``6``, ``7``] ` ` `  `# printing original list  ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Alternate front - rear Sum ` `# using loop ` `res ``=` `[] ` `j ``=` `len``(test_list) ``-` `1` `for` `i ``in` `range``(``0``, ``len``(test_list) ``/``/` `2``): ` `    ``res.append(test_list[i] ``+` `test_list[j]) ` `    ``j ``=` `j ``-` `1` ` `  `# printing result ` `print` `(``"The alterate front - rear Sum list is : "` `+` `str``(res)) `

Output :

```The original list is : [1, 4, 5, 3, 6, 7]
The alterate front - rear Sum list is : [8, 10, 8]
```

Method #2 : Using list comprehension
Naive method can be used to perform, but list comprehension provides a one liner method to perform this task.

 `# Python3 code to demonstrate  ` `# Alternate front - rear Sum ` `# using list comprehension ` ` `  `# initializing list  ` `test_list ``=` `[``1``, ``4``, ``5``, ``3``, ``6``, ``7``] ` ` `  `# printing original list  ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Alternate front - rear Sum ` `# using list comprehension ` `res ``=` `[test_list[i] ``+` `test_list[``len``(test_list) ``-` `(i ``+` `1``)] ``for` `i ``in` `range``(``len``(test_list) ``/``/` `2``)] ` ` `  `# printing result ` `print` `(``"The alterate front - rear Sum list is : "` `+` `str``(res)) `

Output :

```The original list is : [1, 4, 5, 3, 6, 7]
The alterate front - rear Sum list is : [8, 10, 8]
```

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