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LeetCode

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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.)

Code

class Solution {
    public int[] productExceptSelf(int[] nums) {
        int[] res = new int[nums.length];

        res[0] = 1;

        int curr = nums[0];
        for(int i = 1; i < nums.length; i++) {
            res[i] = curr;
            curr *= nums[i];
        }

        curr = nums[nums.length - 1];
        for(int i = nums.length - 2; i >= 0; i--){
            res[i] *= curr;
            curr *= nums[i];
        }

        return res;
    }
}

class Solution:
    def productExceptSelf(self, nums: List[int]) -> List[int]:
        res = []

        for i in range(len(nums)):
            res.append(1)

        curr = nums[0]
        for i in range(1, len(nums)):
            res[i] = curr
            curr *= nums[i]

        curr = nums[-1]
        for i in range(len(nums) - 2, -1, -1):
            res[i] *= curr
            curr *= nums[i]

        return res