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58 lines
1.6 KiB
Python
58 lines
1.6 KiB
Python
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"""Bisection algorithms.
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These algorithms are taken from Python's standard library, and modified so they take a 'key' parameter (similar to how
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`sorted` works).
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"""
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def bisect_right(a, x, lo=0, hi=None, key=None):
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"""Return the index where to insert item x in list a, assuming a is sorted.
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The return value i is such that all e in a[:i] have e <= x, and all e in
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a[i:] have e > x. So if x already appears in the list, a.insert(x) will
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insert just after the rightmost x already there.
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Optional args lo (default 0) and hi (default len(a)) bound the
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slice of a to be searched.
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"""
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if key is None:
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key = lambda x: x
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if lo < 0:
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raise ValueError('lo must be non-negative')
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if hi is None:
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hi = len(a)
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while lo < hi:
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mid = (lo+hi)//2
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if key(x) < key(a[mid]): hi = mid
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else: lo = mid+1
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return lo
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def bisect_left(a, x, lo=0, hi=None, key=None):
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"""Return the index where to insert item x in list a, assuming a is sorted.
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The return value i is such that all e in a[:i] have e < x, and all e in
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a[i:] have e >= x. So if x already appears in the list, a.insert(x) will
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insert just before the leftmost x already there.
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Optional args lo (default 0) and hi (default len(a)) bound the
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slice of a to be searched.
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"""
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if key is None:
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key = lambda x: x
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if lo < 0:
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raise ValueError('lo must be non-negative')
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if hi is None:
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hi = len(a)
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while lo < hi:
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mid = (lo+hi)//2
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if key(a[mid]) < key(x): lo = mid+1
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else: hi = mid
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return lo
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# Create aliases
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bisect = bisect_right
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