益智..将数组X值的求解产品 [英] Puzzle.. solving product of values in array X
问题描述
能否请你帮我解决这个吗?
Can you please help me solving this one?
您有n个整数的无序排列的X.查找包含n个元素,其中Mi为x中所有整数除曦的产品列M。您不得使用部门。您可以使用额外的内存。 (提示:有解决方案比为O(n ^ 2)速度更快。)
You have an unordered array X of n integers. Find the array M containing n elements where Mi is the product of all integers in X except for Xi. You may not use division. You can use extra memory. (Hint: There are solutions faster than O(n^2).)
基本的 - 为O(n ^ 2)和一个用除法是很容易。但我就是不能得到另一种解决方案是为O快(N ^ 2)。
The basic ones - O(n^2) and one using division is easy. But I just can't get another solution that is faster than O(n^2).
推荐答案
让离开[I]
在 X <所有元素的产品/从
1..i
>。让右键[I]
是所有元素中的 X中的产品
从 i..N
。你可以计算无论是在 O(N)
不按以下方式划分:离开[我] =左[我 - 1] * X [我]
和右键[I] =正确的[I + 1] * X [I]
;
Let left[i]
be the product of all elements in X
from 1..i
. Let right[i]
be the product of all elements in X
from i..N
. You can compute both in O(n)
without division in the following way: left[i] = left[i - 1] * X[i]
and right[i] = right[i + 1] * X[i]
;
现在,我们将计算 M
: M [I] =左[我 - 1] *正确的[I + 1]
注:离开
和右键
是数组
希望这是明确的:)
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