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

#include <vector>

class Solution {
public:
    std::vector<int> productExceptSelf(std::vector<int>& nums) {
        int product = 1;
        std::vector<int> ans(nums.size(), 1);

        for (int num : nums) {
            product *= num;
        }

        for (int i = 0; i < nums.size(); i++) {
            if (nums[i] != 0) {
                ans[i] = product / nums[i];
            } else {
                int p = 1;
                for (int j = 0; j < nums.size(); j++) {
                    if (j != i) {
                        p *= nums[j];
                    }
                }
                ans[i] = p;
            }
        }

        return ans;
    }
};