Introduction

In this blog post, we will explore how to solve the LeetCode problem "3427" 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 of size n. For each index i where 0 <= i < n, define a subarray nums[start ... i] where start = max(0, i - nums[i]). Return the total sum of all elements from the subarray defined for each index in the array. Example 1: Input: nums = [2,3,1] Output: 11 Explanation: i Subarray Sum 0 nums[0] = [2] 2 1 nums[0 ... 1] = [2, 3] 5 2 nums[1 ... 2] = [3, 1] 4 Total Sum 11 The total sum is 11. Hence, 11 is the output. Example 2: Input: nums = [3,1,1,2] Output: 13 Explanation: i Subarray Sum 0 nums[0] = [3] 3 1 nums[0 ... 1] = [3, 1] 4 2 nums[1 ... 2] = [1, 1] 2 3 nums[1 ... 3] = [1, 1, 2] 4 Total Sum 13 The total sum is 13. Hence, 13 is the output. Constraints: 1 <= n == nums.length <= 100 1 <= nums[i] <= 1000

Explanation

Here's an efficient solution to the problem:

• Iterate and Calculate Subarray Start: For each index i, calculate the start index of the subarray as max(0, i - nums[i]).
• Sum Subarray Elements: Sum the elements of the subarray from the calculated start index up to the current index i.

• Accumulate Total Sum: Add the subarray sum to a running total, which will be the final result.

• Runtime Complexity: O(n), where n is the length of the input array. Storage Complexity: O(1).

Code

    def subarray_sum(nums):
    """
    Calculates the total sum of elements from subarrays defined for each index.

    Args:
        nums: An integer array.

    Returns:
        The total sum of elements from the subarrays.
    """

    total_sum = 0
    n = len(nums)

    for i in range(n):
        start = max(0, i - nums[i])
        subarray_sum = 0
        for j in range(start, i + 1):
            subarray_sum += nums[j]
        total_sum += subarray_sum

    return total_sum