leetcode_gym/_problems/productOfArrayExceptSelf.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Product of Array Except Self			https://leetcode.com/problems/product-of-array-except-self	Attempted

Problem

Given an array nums of n integers where n > 1,  return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Example:

Input:  [1,2,3,4]
Output: [24,12,8,6]
Constraint: It's guaranteed that the product of the elements of any prefix or suffix of the array (including the whole array) fits in a 32 bit integer.

Note: Please solve it without division and in O(n).

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

Solution

Make Left and Right Array, then multiply together.

• Left Array consist of product of all elements to the left of i
• Right Array consist of product of all elements to the right of i

{% highlight python %}

def productExceptSelf(self, nums: List[int]) -> List[int]:
    
    length = len(nums)
    
    L, R, ans = [0]*length, [0]*length, [0]*length
    
    L[0]=1
    for i in range(1, length):
        L[i] = nums[i-1]*L[i-1]
    
    R[length-1]=1
    for i in range(length-2, -1, -1):
    # for i in reversed(range(length-1)):
        R[i] = nums[i+1] * R[i+1]
    
    
    for i in range(length):
        ans[i] = L[i]*R[i]
    
    return ans

{% endhighlight %}