LeetCode-in-All

238. Product of Array Except Self

Medium

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:

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:

Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)

Solution

public class Solution {
    public int[] ProductExceptSelf(int[] nums) {
        int product = 1;
        int[] ans = new int[nums.Length];
        foreach (int num in nums) {
            product = product * num;
        }
        for (int i = 0; i < nums.Length; i++) {
            if (nums[i] != 0) {
                ans[i] = product / nums[i];
            } else {
                int p = 1;
                for (int j = 0; j < nums.Length; j++) {
                    if (j != i) {
                        p = p * nums[j];
                    }
                }
                ans[i] = p;
            }
        }
        return ans;
    }
}