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44 lines
1.2 KiB
Python
44 lines
1.2 KiB
Python
"""
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File: leetcode_two_sum.py
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Created Time: 2022-11-25
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Author: Krahets (krahets@163.com)
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"""
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import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from modules import *
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def two_sum_brute_force(nums: List[int], target: int) -> List[int]:
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""" 方法一：暴力枚举 """
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# 两层循环，时间复杂度 O(n^2)
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for i in range(len(nums) - 1):
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for j in range(i + 1, len(nums)):
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if nums[i] + nums[j] == target:
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return i, j
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return []
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def two_sum_hash_table(nums: List[int], target: int) -> List[int]:
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""" 方法二：辅助哈希表 """
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# 辅助哈希表，空间复杂度 O(n)
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dic = {}
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# 单层循环，时间复杂度 O(n)
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for i in range(len(nums)):
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if target - nums[i] in dic:
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return dic[target - nums[i]], i
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dic[nums[i]] = i
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return []
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""" Driver Code """
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if __name__ == '__main__':
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# ======= Test Case =======
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nums = [2,7,11,15]
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target = 9
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# ====== Driver Code ======
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# 方法一
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res = two_sum_brute_force(nums, target)
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print("方法一 res =", res)
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# 方法二
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res = two_sum_hash_table(nums, target)
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print("方法二 res =", res)
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