Partition Equal Subset Sum - #102
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お疲れ様です。 Partition Equal Subset Sumに取り組みました。 問題: https://leetcode.com/problems/partition-equal-subset-sum |
nodchip
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Aug 9, 2026
| class Solution: | ||
| def canPartition(self, nums: List[int]) -> bool: | ||
| # dp[i][j]: nums[:i + 1]から選んで和がjとなるsubsetを作れる. 0/1ナップザック | ||
| sum_of_nums = sum(nums) |
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こちらのコメントをご参照ください。
h-masder/Arai60#18 (comment)
| return False | ||
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| target = sum_of_nums // 2 | ||
| dp = [[False] * (target + 1) for _ in range(len(nums))] |
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dp という変数名は Dynamic Programming の略だと思うのですが、読み手にとってあまり有益な情報になっていないように思います。中にどのような値が含まれるかを端的に表した英単語や英語句を付けると良いと思います。 can_make_sum あたりはいかがでしょうか？
| bits = 1 # 和 0 のみ作れる | ||
| for num in nums: | ||
| bits |= bits << num | ||
| return bits >> target & 1 == 1 |
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演算子の優先順位が分かりにくく感じました。適宜 () で優先順位を明示したほうが、読み手にとって読みやすくなると思います。
return (bits >> target) & 1 == 1|
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| bitset DP | ||
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| - 上記一次元DPは[True, False, True, ...]という真偽値の列だが、これを整数1個の各ビットとして表現する |
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この解法は思いつきませんでした。面白い解法だと思います。
Python は int が表現できる範囲に上限が実質ないため、このような書き方ができるのだと思います。また、 CPython では、int は、ある程度の範囲を超えると、多倍長整数として扱われ、桁数に応じた時間計算量と空間計算量がかかる点に注意が必要だと思います。
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Partition Equal Subset Sum
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