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victor-iyi/swap_without_if.py

Created March 31, 2021 06:50
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A function that takes 4 or 7 as input and returns 7 or 4 [f(4) = 7 OR f(7) = 4] WITHOUT USING if-statement
Raw
swap_without_if.py
"""Implement a function which takes an integer which does the following:
- if input is 4: it returns 7
- if input is 7: it returns 4
Otherwise (unspecified).
However:
CANNOT USE `if-statement`.
To Run:
- Make sure you `pip install pytest`.
Then:
```$ pytest -v swap_without_if.py```
"""
import pytest
from typing import Dict
def f_ternary(x: int) -> int:
"""Uses an `if-expression` not if statement.
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return 7 if x == 4 else 4
def f_old_ternary(x: int) -> int:
"""Uses ternary operator.
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return x == 4 and 7 or 4
def f_dict(x: int) -> int:
"""Uses dictionary indexing.
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return {4: 7, 7: 4}[x]
# Uses one-liner dictionary indexing.
f_dict2: Dict[int, int] = {4: 7, 7: 4}.__getitem__
def f_list(x: int) -> int:
"""Uses a list indexing.
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return [0, 0, 0, 0, 7, 0, 0, 4][x]
def f_addition(x: int) -> int:
"""Uses integer addtion/subtraction.
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return 11 - x
def f_bitflip(x: int) -> int:
"""Using a clever bit flip operation.
Note:
```python
>>> bin(4)
'0b100'
>>> bin(7)
'0b111'
>>> bin(4 ^ 0b11) # == 7
'0b111'
>>> bin(7 ^ 0b11) # == 4
'0b100'
```
Args:
x (int) - Given either 4 or 7.
Return:
int -- Flips the input.
f(4) = 7
f(7) = 4
"""
assert x == 4 or x == 7, "input must be 4 or 7"
return x ^ 0b11
# `pytest` mark decorator for creating parameters.
params = pytest.mark.parametrize(
'f',
(
f_ternary,
f_old_ternary,
f_dict,
f_dict2,
f_list,
f_addition,
f_bitflip,
),
)
@params
def test_4_returns_7(f):
assert f(4) == 7
with pytest.raises((AssertionError, KeyError)):
f(2)
@params
def test_7_returns_4(f):
assert f(7) == 4
with pytest.raises((AssertionError, KeyError)):
f(2)
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