2024-03-15 Daily Challenge

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In: DailyChallenge

Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 15

Description

Product of Array Except Self

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:

  • 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.

 

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

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  vector<int> productExceptSelf(vector<int>& nums) {
    int sum = nums[0];
    int n = nums.size();
    vector<int> ans(n);
    ans[0] = 1;

    for(int i = 1; i < n; ++i){
      ans[i] = sum;
      sum = sum * nums[i];
    }

    sum = 1;

    for(int i = n - 1; i >= 0; --i){
      ans[i] = ans[i] * sum;
      sum = sum * nums[i];
    }

    return ans;
  }
};

// Accepted
// 20/20 cases passed (8 ms)
// Your runtime beats 99.98 % of cpp submissions
// Your memory usage beats 56.08 % of cpp submissions (24.1 MB)
Algorithm