Introduction

In this blog post, we will explore how to solve the LeetCode problem "985" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given an integer array nums and an array queries where queries[i] = [vali, indexi]. For each query i, first, apply nums[indexi] = nums[indexi] + vali, then print the sum of the even values of nums. Return an integer array answer where answer[i] is the answer to the ith query. Example 1: Input: nums = [1,2,3,4], queries = [[1,0],[-3,1],[-4,0],[2,3]] Output: [8,6,2,4] Explanation: At the beginning, the array is [1,2,3,4]. After adding 1 to nums[0], the array is [2,2,3,4], and the sum of even values is 2 + 2 + 4 = 8. After adding -3 to nums[1], the array is [2,-1,3,4], and the sum of even values is 2 + 4 = 6. After adding -4 to nums[0], the array is [-2,-1,3,4], and the sum of even values is -2 + 4 = 2. After adding 2 to nums[3], the array is [-2,-1,3,6], and the sum of even values is -2 + 6 = 4. Example 2: Input: nums = [1], queries = [[4,0]] Output: [0] Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 1 <= queries.length <= 104 -104 <= vali <= 104 0 <= indexi < nums.length

Explanation

Here's a breakdown of the solution, followed by the Python code:

• High-Level Approach:

  • Calculate the initial sum of even numbers in nums.
  • Iterate through each query, updating the nums array in place and adjusting the even sum based on whether the modified number was even before and after the update.
  • Append the updated even sum to the result array after each query.

• Complexity:

  • Runtime: O(N + Q), where N is the length of nums and Q is the length of queries. This is because we iterate through nums once to calculate the initial even sum and then iterate through queries once.
  • Storage: O(Q), where Q is the length of queries because the result array scales linearly with the number of queries.

Code

    def sum_even_after_queries(nums, queries):
    """
    Calculates the sum of even values in nums after each query.

    Args:
        nums: An integer array.
        queries: An array of queries where queries[i] = [vali, indexi].

    Returns:
        An integer array where answer[i] is the answer to the ith query.
    """

    even_sum = 0
    for num in nums:
        if num % 2 == 0:
            even_sum += num

    answer = []
    for val, index in queries:
        if nums[index] % 2 == 0:
            even_sum -= nums[index]

        nums[index] += val

        if nums[index] % 2 == 0:
            even_sum += nums[index]

        answer.append(even_sum)

    return answer