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Product of Array Except Self

Question​

None

Example 1
Input: [1,2,3,4]

Output: [24,12,8,6]

Solution​

all//Product of Array Except Self.py


def productExceptSelf(nums):
    # The length of the input array
    length = len(nums)

    # The answer array to be returned
    answer = [0]*length

    # answer[i] contains the product of all the elements to the left
    # Note: for the element at index '0', there are no elements to the left,
    # so the answer[0] would be 1
    answer[0] = 1
    for i in range(1, length):

        # answer[i - 1] already contains the product of elements to the left of 'i - 1'
        # Simply multiplying it with nums[i - 1] would give the product of all
        # elements to the left of index 'i'
        answer[i] = nums[i - 1] * answer[i - 1]

    # R contains the product of all the elements to the right
    # Note: for the element at index 'length - 1', there are no elements to the right,
    # so the R would be 1
    R = 1;
    for i in reversed(range(length)):

        # For the index 'i', R would contain the
        # product of all elements to the right. We update R accordingly
        answer[i] = answer[i] * R
        R *= nums[i]

    return answer