LeetCode 75 - 238. Product of Array Except Self

Description

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]

Constraints:

2 <= nums.length <= 10^5
-30 <= nums[i] <= 30
The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

Solutions

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        int length = nums.size();

        vector<int> L(length, 0), R(length, 0);
        vector<int> answer(length);

        L[0] = 1;
        for (int i = 1; i < length; i++) {
            L[i] = nums[i - 1] * L[i - 1];
        }

        R[length - 1] = 1;
        for (int i = length - 2; i >= 0; i--) {
            R[i] = nums[i + 1] * R[i + 1];
        }

        for (int i = 0; i < length; i++) {
            answer[i] = L[i] * R[i];
        }

        return answer;
    }
};