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Python Challenges: Find two elements once in a list where every element appears exactly twice in the list

Python Challenges - 1: Exercise-15 with Solution

Write a Python program to find two elements once in a list where every element appears exactly twice in the list.

Explanation :

Python: Find two elements once in a list where every element appears exactly twice in the list

Sample Solution:

Python Code:

import functools
import operator
def two_numbers(arr):
    x_xor_y = functools.reduce(operator.xor, arr)
    bit =  x_xor_y & -x_xor_y
    result = [0, 0]
    for i in arr:
        result[bool(i & bit)] ^= i
    return result

print(two_numbers([1, 2, 1, 3, 2, 5]))
print(two_numbers([11, 5, 3, 7, 0, 5, 3, 6, 7, 11]))

Sample Output:

[5, 3]
[0, 6]

Flowchart:

Python Flowchart: Find two elements once in a list where every element appears exactly twice in the list

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Previous: Write a Python program to find the single element appears once in a list where every element appears four times except for one.
Next: Write a Python program to add the digits of a positive integer repeatedly until the result has a single digit.

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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