#### Linear Search

A
J
E
E
L
Y 45 más contribuidores
```"""
This is pure Python implementation of linear search algorithm

For doctests run following command:
python3 -m doctest -v linear_search.py

For manual testing run:
python3 linear_search.py
"""

def linear_search(sequence: list, target: int) -> int:
"""A pure Python implementation of a linear search algorithm

:param sequence: a collection with comparable items (as sorted items not required
in Linear Search)
:param target: item value to search
:return: index of found item or None if item is not found

Examples:
>>> linear_search([0, 5, 7, 10, 15], 0)
0
>>> linear_search([0, 5, 7, 10, 15], 15)
4
>>> linear_search([0, 5, 7, 10, 15], 5)
1
>>> linear_search([0, 5, 7, 10, 15], 6)
-1
"""
for index, item in enumerate(sequence):
if item == target:
return index
return -1

def rec_linear_search(sequence: list, low: int, high: int, target: int) -> int:
"""
A pure Python implementation of a recursive linear search algorithm

:param sequence: a collection with comparable items (as sorted items not required
in Linear Search)
:param low: Lower bound of the array
:param high: Higher bound of the array
:param target: The element to be found
:return: Index of the key or -1 if key not found

Examples:
>>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 0)
0
>>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 700)
4
>>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 30)
1
>>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, -6)
-1
"""
if not (0 <= high < len(sequence) and 0 <= low < len(sequence)):
raise Exception("Invalid upper or lower bound!")
if high < low:
return -1
if sequence[low] == target:
return low
if sequence[high] == target:
return high
return rec_linear_search(sequence, low + 1, high - 1, target)

if __name__ == "__main__":
user_input = input("Enter numbers separated by comma:\n").strip()
sequence = [int(item.strip()) for item in user_input.split(",")]

target = int(input("Enter a single number to be found in the list:\n").strip())
result = linear_search(sequence, target)
if result != -1:
print(f"linear_search({sequence}, {target}) = {result}")
else:
print(f"{target} was not found in {sequence}")
```

#### Declaración de problema

Dada una matriz de `n` elementos, escriba una función para buscar el índice de un elemento determinado (destino)

#### Enfoque

• Comience a iterar con el primer elemento de la matriz.
• Compararlo con el elemento objetivo.
• Si es igual al elemento de destino, devuelva el índice.
• De lo contrario, continúe iterando.
• Devolver -1 si el elemento de destino no se encuentra en la matriz.

#### Complejidad temporal

`O(n)` Peor caso `O(1)` Mejor caso (Si el primer elemento de matriz es el elemento de destino)

`O(1)`

#### Ejemplo

``````arr = [1, 3, 9, 5, 0, 2]

target = 5
La búsqueda lineal debe devolver el índice 3, ya que 5 está en el índice 3.

target = 6
La búsqueda lineal debe devolver -1 ya que 6 no está presente en la matriz
``````

#### Explicación en YouTube

Un vídeo CS50 que explica el algoritmo de búsqueda lineal