81 lines
2.3 KiB
Python
81 lines
2.3 KiB
Python
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"""Bisection algorithms."""
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def insort_right(a, x, lo=0, hi=None):
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"""Insert item x in list a, and keep it sorted assuming a is sorted.
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If x is already in a, insert it to the right of the rightmost x.
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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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lo = bisect_right(a, x, lo, hi)
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a.insert(lo, x)
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def bisect_right(a, x, lo=0, hi=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 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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# Use __lt__ to match the logic in list.sort() and in heapq
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if x < a[mid]: hi = mid
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else: lo = mid+1
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return lo
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def insort_left(a, x, lo=0, hi=None):
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"""Insert item x in list a, and keep it sorted assuming a is sorted.
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If x is already in a, insert it to the left of the leftmost x.
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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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lo = bisect_left(a, x, lo, hi)
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a.insert(lo, x)
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def bisect_left(a, x, lo=0, hi=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 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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# Use __lt__ to match the logic in list.sort() and in heapq
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if a[mid] < x: lo = mid+1
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else: hi = mid
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return lo
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# Overwrite above definitions with a fast C implementation
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try:
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from _bisect import *
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except ImportError:
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pass
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# Create aliases
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bisect = bisect_right
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insort = insort_right
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