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43 lines
1.1 KiB
Python
43 lines
1.1 KiB
Python
"""
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File: 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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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，时间复杂度为 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，空间复杂度为 O(n)
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dic = {}
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# 单层循环，时间复杂度为 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 = 13
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# ====== Driver Code ======
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# 方法一
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res: list[int] = 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: list[int] = two_sum_hash_table(nums, target)
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print("方法二 res =", res)
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