Python Challenges: Find the single element in a list where every element appears three times except for one

Last update on May 28 2022 13:42:24 (UTC/GMT +8 hours)

Python Challenges - 1: Exercise-13 with Solution

Write a Python program to find the single element in a list where every element appears three times except for one.

Explanation:

Python: Find the single element in a list where every element appears three times except for one.

Sample Solution:-

Python Code:

def single_number(arr):
    ones, twos = 0, 0
    for x in arr:
        ones, twos = (ones ^ x) & ~twos, (ones & x) | (twos & ~x)
    assert twos == 0
    return ones
arr1 = [5, 3, 4, 3, 5, 5, 3]
arr2 = [-1, 1, 1, -1, -1, 1, 0]
print(single_number(arr1))
print(single_number(arr2))

Sample Output:

4                                                                        
0

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Previous: Write a Python program to find the single number in a list that doesn't occur twice.
Next: Write a Python program to find the single element appears once in a list where every element appears four times except for one.

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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