LeetCode #238: Product of Array Except Self (C/C++).

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source: https://leetcode.com/problems/product-of-array-except-self/
C/C++ Solution to LeetCode problem 238. Product of Array Except Self.

Problem

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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.

Examples

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Example 1:

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

Example 2:

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

Constraints

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• 2 <= nums.length <= 105
• -30 <= nums[i] <= 30
• The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

Solution

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class Solution {
public:
  vector<int> productExceptSelf(vector<int>& nums) {
    int s = nums.size() - 1;
    vector<int> sol(nums.size(), 1);
    vector<int> tmp(nums.size(), 1);

    for(int i=1; i<nums.size(); i+=1) {
      int l = nums[i - 1];
      int r = nums[(s - i) + 1];

      sol[i] = sol[i-1]*l;
      tmp[s-i] = tmp[(s-i) + 1] * r;
    }

    for(int i=0; i<nums.size(); i+=1)
      sol[i] *= tmp[i];

    return sol;
  }
};