Linear Search
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"""
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 -1 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}")
关于这个算法
Problem Statement
Given an array of n elements, write a function to search for the index of a given element (target)
Approach
- Start iterating with the first element in the array.
- Compare it with the target element
- If it is equal to the target element then return the index
- Else continue iterating
- Return -1 if target element is not found in the array
Time Complexity
O(n) Worse Case
O(1) Best Case (If first element of array is the target element)
Space Complexity
O(1)
Example
arr = [1, 3, 9, 5, 0, 2]
target = 5
Linear Search should return index 3 as 5 is on index 3
target = 6
Linear Search should return -1 as 6 is not present in the array
Video Explanation
A CS50 video explaining the Linear Search Algorithm
