December 2016
Intermediate to advanced
440 pages
9h 44m
Japanese
Content preview from アルゴリズムクイックリファレンス 第2版
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110
■
5
章 探索
5.2.5
変形
「探索（して見つからなかったら）挿入」という操作を行う場合は、配列の添字が
非負であることに注目する。次に示す
Python
の例では、メソッド
bs_contains
が、
整列配列の中に目標要素
target
がないときは、負数
p
を返す。
bs_insert
からわか
るように、値−
(p
＋
1)
が、
target
を挿入する添字の位置を示す。当然ながら、こ
れより添字の大きい要素は右へ移されて、新たな要素のために場所を空ける。
例
5-4
Python
の探索挿入
def bs_contains(ordered, target):
""" target
の添字か挿入位置
-(p+1)
を返す
"""
low = 0
high = len(ordered)-1
while low <= high:
mid = (low + high) // 2
if target == ordered[mid]:
return mid
elif target < ordered[mid]:
high = mid-1
else:
low = mid+1
return -(low + 1)
def bs_insert(ordered, target):
"""
存在しなければ、
target
を適切な位置に挿入する
"""
idx = bs_contains(ordered, target)
if idx < 0:
ordered.insert(-(idx + 1), target)
整列配列での挿入削除は
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