hello-algo/codes/python/chapter_computational_complexity/leetcode_two_sum.py
Yudong Jin 8918ec9079
refactor: Follow the PEP 585 Typing standard (#439)
* Follow the PEP 585 Typing standard

* Update list.py
2023-03-23 18:51:56 +08:00

40 lines
1.1 KiB
Python

"""
File: leetcode_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]:
""" 方法一:暴力枚举 """
# 两层循环,时间复杂度 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]:
""" 方法二:辅助哈希表 """
# 辅助哈希表,空间复杂度 O(n)
dic = {}
# 单层循环,时间复杂度 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 = 9
# ====== Driver Code ======
# 方法一
res: list[int] = two_sum_brute_force(nums, target)
print("方法一 res =", res)
# 方法二
res: list[int] = two_sum_hash_table(nums, target)
print("方法二 res =", res)