Python: Sort the numbers by the sum of their digits

Last update on May 28 2022 13:41:46 (UTC/GMT +8 hours)

Python Programming Puzzles: Exercise-38 with Solution

Write a Python program to sort the numbers of a given list by the sum of their digits.

Input: 
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] 
Output:
[10, 11, 20, 12, 13, 14, 15, 16, 17, 18, 19]

Input: 
[23, 2, 9, 34, 8, 9, 10, 74] 
Output:
[10, 2, 23, 34, 8, 9, 9, 74]

Pictorial Presentation:

Python: Sort the numbers by the sum of their digits.

Sample Solution-1:

Python Code:

#License: https://bit.ly/3oLErEI

def test(nums):
     return sorted(nums, key=lambda n: sum(int(c) for c in str(n) if c != "-"))
 
nums = [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
print("Original list of numbers:",nums)
print("Sort the numbers of the said list by the sum of their digits:")
print(test(nums))
nums = [23,2,9,34,8,9,10,74]
print("\nOriginal list of numbers:",nums)
print("Sort the numbers of the said list by the sum of their digits:")
print(test(nums))

Sample Output:

Original list of numbers: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
Sort the numbers of the said list by the sum of their digits:
[10, 11, 20, 12, 13, 14, 15, 16, 17, 18, 19]

Original list of numbers: [23, 2, 9, 34, 8, 9, 10, 74]
Sort the numbers of the said list by the sum of their digits:
[10, 2, 23, 34, 8, 9, 9, 74]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Sample Solution-2:

Python Code:

#License: https://bit.ly/3oLErEI

def test(nums):
    unordered = nums.copy()
    ordered = []
    while unordered:
        # The number that comes first, since the list is sorted by the primes
        smallest = unordered[0]
        s = sum(int(c) for c in str(smallest) if c != "-")
        for t in unordered:
            t_s = sum(int(c) for c in str(t) if c != "-")
            if t_s < s:
                smallest = t
                s = t_s
        ordered.append(smallest)
        unordered.remove(smallest)
    return ordered
 
nums = [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
print("Original list of numbers:",nums)
print("Sort the numbers of the said list by the sum of their digits:")
print(test(nums))
nums = [23,2,9,34,8,9,10,74]
print("\nOriginal list of numbers:",nums)
print("Sort the numbers of the said list by the sum of their digits:")
print(test(nums))

Sample Output:

Original list of numbers: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
Sort the numbers of the said list by the sum of their digits:
[10, 11, 20, 12, 13, 14, 15, 16, 17, 18, 19]

Original list of numbers: [23, 2, 9, 34, 8, 9, 10, 74]
Sort the numbers of the said list by the sum of their digits:
[10, 2, 23, 34, 8, 9, 9, 74]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor :

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Next: Determine which triples sum to zero.

Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

The os and os.path modules.

The __file__ constant

os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")

os.path.dirname(path) (returns "the directory name of pathname path")

os.getcwd() (returns "a string representing the current working directory")

os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m