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69 lines
2.3 KiB
69 lines
2.3 KiB
def binary_search(arr, target):
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left = 0;
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right = len(arr) - 1
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while left <= right:
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mid = left + (right - left) // 2;
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if arr[mid] == target:
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return mid
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elif arr[mid] < target:
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left = mid + 1
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else:
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right = mid - 1
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return -1
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def bisect_left(arr, target):
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"""Returns the leftmost position that `target` should
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go to such that the sequence remains sorted."""
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left = 0
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right = len(arr)
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while left < right:
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mid = (left + right) // 2
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if arr[mid] < target:
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left = mid + 1
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else:
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right = mid
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return left
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def bisect_right(arr, target):
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"""Returns the rightmost position that `target` should
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go to such that the sequence remains sorted."""
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left = 0
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right = len(arr)
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while left < right:
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mid = (left + right) // 2
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if arr[mid] > target:
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right = mid
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else:
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left = mid + 1
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return left
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print(binary_search([1, 2, 3, 10], 1) == 0)
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print(binary_search([1, 2, 3, 10], 2) == 1)
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print(binary_search([1, 2, 3, 10], 3) == 2)
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print(binary_search([1, 2, 3, 10], 10) == 3)
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print(binary_search([1, 2, 3, 10], 9) == -1)
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print(binary_search([1, 2, 3, 10], 4) == -1)
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print(binary_search([1, 2, 3, 10], 0) == -1)
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print(binary_search([1, 2, 3, 10], 11) == -1)
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print(binary_search([5, 7, 8, 10], 3) == -1)
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print(bisect_left([1, 2, 3, 3, 10], 1) == 0)
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print(bisect_left([1, 2, 3, 3, 10], 2) == 1)
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print(bisect_left([1, 2, 3, 3, 10], 3) == 2) # First "3" is at index 2
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print(bisect_left([1, 2, 3, 3, 10], 10) == 4)
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# These return a valid index despite target not being in array.
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print(bisect_left([1, 2, 3, 3, 10], 9) == 4)
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print(bisect_left([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
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print(bisect_left([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
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print(bisect_right([1, 2, 3, 3, 10], 1) == 1)
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print(bisect_right([1, 2, 3, 3, 10], 2) == 2)
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print(bisect_right([1, 2, 3, 3, 10], 3) == 4) # Last "3" is at index 3, so insert new "3" at index 4
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print(bisect_right([1, 2, 3, 3, 10], 10) == 5)
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# These return a valid index despite target not being in array.
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print(bisect_right([1, 2, 3, 3, 10], 9) == 4)
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print(bisect_right([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
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print(bisect_right([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
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