【Arai60】24問目 108_Convert Sorted Array to Binary Search Tree#24
Merged
shining-ai merged 2 commits intomainfrom Jun 30, 2024
Merged
【Arai60】24問目 108_Convert Sorted Array to Binary Search Tree#24shining-ai merged 2 commits intomainfrom
shining-ai merged 2 commits intomainfrom
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hayashi-ay
reviewed
Mar 14, 2024
| root = TreeNode(nums[mid]) | ||
| queue = deque([(root, (0, mid - 1), (mid + 1, len(nums) - 1))]) | ||
| while queue: | ||
| node, left_range, right_range = queue.popleft() |
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parentとかでもいいかも。
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| node, left_range, right_range = queue.popleft() | |
| parent, left_range, right_range = queue.popleft() |
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BFSの方はparentの方が分かりやすいですね。
| queue = deque([(root, (0, mid - 1), (mid + 1, len(nums) - 1))]) | ||
| while queue: | ||
| node, left_range, right_range = queue.popleft() | ||
| if left_range[0] <= left_range[1]: |
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関数に切り出すとかしても良いかも。うまく切り出せるかは試してないですが。
| node.right = helper(mid + 1, right) | ||
| return node | ||
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| return helper(0, len(nums) - 1) |
| class Solution: | ||
| def sortedArrayToBST(self, nums: List[int]) -> Optional[TreeNode]: | ||
| mid = (len(nums) - 1) // 2 | ||
| root = TreeNode(nums[mid]) |
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LeetCodeの制約ではlen(nums) >= 1が保証されてますが、空配列だとIndexErrorになりますね。
| def helper(left, right): | ||
| if left > right: | ||
| return None | ||
| mid = (left + right) // 2 |
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コードからは意識してるか分からなかったので念の為共有です。範囲に含まれる要素が偶数のときに真ん中が存在しないのでmidの選択により左と右のどちらをrootにするかが決まりますね。
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問題
https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/