238. Product of Array Except Self [medium] (Python)

Topic links

https://leetcode.com/problems/product-of-array-except-self/

Original title

Given an array of n integers where n > 1, nums and return an array such that's equal to the product of all output output[i] t He elements of nums except nums[i] .

Solve it without division and in O (n).
For example, given [1,2,3,4] , return [24,12,8,6] .

Follow up:
Could solve it with constant space complexity? (note:the output array does not count as extra space for the purpose of space complexity analysis.)

Method of Thinking Idea one

To facilitate the opening of ideas, not to consider the "follow up" requirements. The time complexity of O (n) is not possible with division, so multiplication cannot be done too much. Consider the first positive and negative two traversal, a traversal of each number to the left of the product of all numbers, a single traversal of each number to the right of the product of all numbers, the last two parts of the product multiplication is obtained.
The following code uses an additional two arrays, the spatial complexity of O (n).

Code

 class solution(object):     def productexceptself(self, nums):        "" : Type Nums:list[int]: rtype:list[int] "" "Res, leftmul, Rightmul = [0]*len (Nums), [0]*len (Nums), [0]*len (nums) leftmul[0] = Rightmul[len (nums)-1] =1         forIinchXrange1, Len (nums)): leftmul[i] = leftmul[i-1] * nums[i-1] forIinchXrange (Len (nums)-2, -1, -1): rightmul[i] = rightmul[i+1] * nums[i+1] forIinchXrange (Len (nums)): res[i] = leftmul[i] * Rightmul[i]returnRes

Idea two

On the basis of the above, actually using the array to store the left and right product is not necessary, with temporary variables can be, so there is the following O (1) spatial complexity of the solution.

Code

 class solution(object):     def productexceptself(self, nums):        "" : Type Nums:list[int]: rtype:list[int] "" "res = [0]*len (nums) tmp =1         forIinchXrange (Len (nums)): res[i] = tmp tmp *= nums[i] tmp =1         forIinchXrange (Len (nums)-1, -1, -1): Res[i] *= tmp tmp *= nums[i]returnRes

PS: Write wrong or write not clear please help point out, thank you!
Reprint Please specify: http://blog.csdn.net/coder_orz/article/details/52071951

238. Product of Array Except Self [medium] (Python)