238. Product of Array Except Self

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

You must write an algorithm that runs in O(n) time and without using the division operation.

Example 1:

1 2	Input: nums = [1,2,3,4] Output: [24,12,8,6]

Example 2:

1 2	Input: nums = [-1,1,0,-3,3] Output: [0,0,9,0,0]

題目不能用除法，只要先算出向右跟向左2個array相乘即可。

T:O(n), S:O(n)
class Solution(object):
    def productExceptSelf(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        n = len(nums)
        temp = 1
        res = [0 for i in range(n)]
        res[0] = 1
        for i in range(1, n):
            res[i] = res[i-1]*nums[i-1]
        for i in range(n-2,-1,-1):
            temp*=nums[i+1]
            res[i] *=temp
        return res

ref

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