Medium Difficulty
Product of Array except Self


Prefix Sum


Product of Array Except Self

Link to algo

To solve this problem, we can use the concept of prefix and suffix products. We'll create two arrays: prefix and suffix.

The prefix array will store the product of all elements to the left of nums[i], and the suffix array will store the product of all elements to the right of nums[i].

We can then calculate the answer array by multiplying prefix[i] with suffix[i] for each index i.

Here's the JavaScript code that implements this algorithm:

function productExceptSelf(nums) {
  const n = nums.length;
  const prefix = new Array(n);
  const suffix = new Array(n);
  const answer = new Array(n);
  // Calculate prefix products
  prefix[0] = 1;
  for (let i = 1; i < n; i++) {
    prefix[i] = prefix[i - 1] * nums[i - 1];
  // Calculate suffix products
  suffix[n - 1] = 1;
  for (let i = n - 2; i >= 0; i--) {
    suffix[i] = suffix[i + 1] * nums[i + 1];
  // Calculate answer array
  for (let i = 0; i < n; i++) {
    answer[i] = prefix[i] * suffix[i];
  return answer;

The time complexity of this algorithm is O(n) because we iterate over the array three times, and each iteration takes linear time. The space complexity is also O(n) because we use three additional arrays of the same length as the input array.

Note that the solution avoids using division and guarantees that the product of any prefix or suffix of nums will fit in a 32-bit integer, as specified in the problem statement.