mirror of
https://github.com/krahets/hello-algo.git
synced 2026-11-10 16:00:36 +08:00
14c314c08c
* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
43 lines
1.2 KiB
Python
43 lines
1.2 KiB
Python
"""
|
|
File: two_sum.py
|
|
Created Time: 2022-11-25
|
|
Author: krahets (krahets@163.com)
|
|
"""
|
|
|
|
|
|
def two_sum_brute_force(nums: list[int], target: int) -> list[int]:
|
|
"""Method 1: brute-force enumeration"""
|
|
# Two nested loops give a time complexity of O(n^2)
|
|
for i in range(len(nums) - 1):
|
|
for j in range(i + 1, len(nums)):
|
|
if nums[i] + nums[j] == target:
|
|
return [i, j]
|
|
return []
|
|
|
|
|
|
def two_sum_hash_table(nums: list[int], target: int) -> list[int]:
|
|
"""Method 2: auxiliary hash table"""
|
|
# The auxiliary hash table uses O(n) space
|
|
dic = {}
|
|
# A single loop with average O(1) hash operations gives an average time complexity of O(n)
|
|
for i in range(len(nums)):
|
|
if target - nums[i] in dic:
|
|
return [dic[target - nums[i]], i]
|
|
dic[nums[i]] = i
|
|
return []
|
|
|
|
|
|
"""Driver code"""
|
|
if __name__ == "__main__":
|
|
# ======= Test case =======
|
|
nums = [2, 7, 11, 15]
|
|
target = 13
|
|
|
|
# ====== Driver code ======
|
|
# Method 1
|
|
res: list[int] = two_sum_brute_force(nums, target)
|
|
print("Method 1: res =", res)
|
|
# Method 2
|
|
res: list[int] = two_sum_hash_table(nums, target)
|
|
print("Method 2: res =", res)
|