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Merge pull request #108 from jerryderry/bsearch-variant-python

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Binary search variants in python
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wangzheng0822 2018-10-26 10:38:33 +08:00 committed by GitHub
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python/16_bsearch/bsearch_variants.py Normal file
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"""
Author: Wenru
"""
from typing import List
def bsearch_left(nums: List[int], target: int) -> int:
"""Binary search of the index of the first element
equal to a given target in the ascending sorted array.
If not found, return -1.
"""
low, high = 0, len(nums) - 1
while low <= high:
mid = low + (high - low) // 2
if nums[mid] < target:
low = mid + 1
else:
high = mid - 1
return low if nums[low] == target else -1
def bsearch_right(nums: List[int], target: int) -> int:
"""Binary search of the index of the last element
equal to a given target in the ascending sorted array.
If not found, return -1.
"""
low, high = 0, len(nums) - 1
while low <= high:
mid = low + (high - low) // 2
if nums[mid] <= target:
low = mid + 1
else:
high = mid - 1
return high if nums[high] == target else -1
def bsearch_left_not_less(nums: List[int], target: int) -> int:
"""Binary search of the index of the first element
not less than a given target in the ascending sorted array.
If not found, return -1.
"""
low, high = 0, len(nums) - 1
while low <= high:
mid = low + (high - low) // 2
if nums[mid] < target:
low = mid + 1
else:
high = mid - 1
return low if low < len(nums) else -1
def bsearch_right_not_greater(nums: List[int], target: int) -> int:
"""Binary search of the index of the last element
not greater than a given target in the ascending sorted array.
If not found, return -1.
"""
low, high = 0, len(nums) - 1
while low <= high:
mid = low + (high - low) // 2
if nums[mid] <= target:
low = mid + 1
else:
high = mid - 1
return high if high > 0 else -1
if __name__ == "__main__":
import bisect
a = [0, 1, 1, 2, 3, 4, 5, 6, 6, 7, 8, 8, 10, 10, 10]
b = [11, 12, 12, 13, 14, 14, 15, 15]
print(bisect.bisect_left(a, 10) == bsearch_left(a, 10))
print(bisect.bisect_right(a, 10))
print(bisect.bisect_right(a, 6)-1 == bsearch_right(a, 6))
print(bisect.bisect_right(b, 14)-1 == bsearch_right(b, 14))
print(bsearch_left_not_less(a, 11))
print(bsearch_right_not_greater(b, 12))
print(bsearch_right_not_greater(b, 10))
print(bsearch_right_not_greater(b, 17))