bisect 模块

"""Bisection algorithms."""


def insort(a, x, lo=0, hi=None, key=None):
    """Insert item x in list a, and keep it sorted assuming a is sorted.

    If x is already in a, insert it to the right of the rightmost x.

    Optional args lo (default 0) and hi (default len(a)) bound the
    slice of a to be searched. key (default None) defines an operation on the item before comparison.
    """
    if not key:
        def key(x): return x
    if lo < 0:
        raise ValueError('lo must be non-negative')
    if hi is None:
        hi = len(a)
    while lo < hi:
        mid = (lo+hi)//2
        if key(x) < key(a[mid]):
            hi = mid
        else:
            lo = mid+1
    a.insert(lo, x)


def bisect_right(a, x, lo=0, hi=None, key=None):
    """Return the index where to insert item x in list a, assuming a is sorted.

    The return value i is such that all e in a[:i] have e <= x, and all e in
    a[i:] have e > x.  So if x already appears in the list, a.insert(x) will
    insert just after the rightmost x already there.

    Optional args lo (default 0) and hi (default len(a)) bound the
    slice of a to be searched. key (default None) defines an operation on the item before comparison.
    """
    if not key:
        def key(x): return x

    if lo < 0:
        raise ValueError('lo must be non-negative')
    if hi is None:
        hi = len(a)
    while lo < hi:
        mid = (lo+hi)//2
        if x < key(a[mid]):
            hi = mid
        else:
            lo = mid+1
    return lo


def search(a, x, lo=0, hi=None, key=None):
    if not key:
        def key(x): return x
    index = bisect_right(a, x, lo, hi, key)
    if index == 0:
        return None
    else:
        searched = a[index-1]
        if key(searched) == x:
            return searched
        else:
            return None