Leetcode 1685. Sum of Absolute Differences in a Sorted Array  Summary and Q&A
TL;DR
The video explains an efficient algorithm to compute the sum of absolute differences in a sorted array.
Key Insights
 ❓ The problem involves calculating absolute differences in sorted arrays, an important concept in algorithm challenges.
 ❓ Utilizing properties of sorted arrays can significantly optimize calculations, reducing complexity from O(n^2) to O(n).
 ↔️ The introduction of left and right sums allows for efficient computation of differences while iterating through the array.
 🧡 Cumulative sums are a powerful technique for solving problems involving ranges and differences in arrays.
 👨💻 The process emphasizes the importance of crafting clear and maintainable code while implementing algorithmic solutions.
 ⌛ Time complexity analysis is crucial for assessing the feasibility of algorithm implementations against input size constraints.
 🎮 The video illustrates how to encapsulate different summation sections into simple variables to streamline the solution.
Transcript
hey there welcome back to lead coding in this video we will be solving the second question of lead code biweekly contest 41 name of the problem is sum of absolute differences in the sorted array you are given an integer area numbers sorted in nondecreasing order build and return an integer array result with the same length as nums such that result... Read More
Questions & Answers
Q: What is the problem statement discussed in the video?
The video addresses the problem titled "Sum of Absolute Differences in a Sorted Array." It requires calculating for each element in a sorted array the sum of absolute differences between that element and all other elements. A straightforward implementation would be inefficient, thus prompting an exploration of optimal solutions.
Q: Why is a naive O(n^2) solution not ideal for this problem?
The naive approach involves direct pairwise computations, leading to a time complexity of O(n^2). Given that the input size can be large, this results in significant performance issues. An efficient solution is necessary to handle higher constraints, thus the presenter shifts focus to an O(n) optimization.
Q: How does the presenter utilize the properties of a sorted array?
The presenter effectively uses the nondecreasing order of the array to simplify calculations. By recognizing that all elements preceding a current index are less than or equal to the current element, the solution leverages this property to separate the sum into contributions from both left and right segments efficiently.
Q: What is the final approach proposed in the video to solve the problem?
The approach involves calculating a total sum of the array, then iterating through it while maintaining a left sum variable. Using this structure, the video describes how to compute sums for both left and right segments efficiently, yielding an O(n) time complexity for the entire solution.
Q: How is the left sum calculated during iteration?
During iteration, the left sum is maintained as each element is processed. It includes the sum of all elements to the left of the current index. This cumulative sum allows for rapid calculation of the sum of absolute differences by factoring in how many elements exist to the left compared to the current number.
Q: What are the time and space complexities of the final solution provided?
The solution achieves O(n) time complexity for both calculating total sums and deriving the result for each index in a single iteration. Regarding space complexity, the implementation only requires additional space for the result array, leading to a constant space complexity when excluding that.
Q: How does the solution compute the right sum during the iteration?
The right sum is derived by subtracting the current left sum and the element at the current index from the total sum. This allows for the efficient calculation of how many elements are on the right and their contributions to the absolute differences relative to the current index.
Q: What recommendation does the presenter make at the end of the video?
The presenter encourages viewers to subscribe to the channel and enable notifications to keep up with future videos. This emphasizes community building and providing ongoing educational content about algorithms and coding challenges.
Summary & Key Takeaways

The problem involves building an integer array where each element is the sum of absolute differences between a given sorted array and every other element.

A naive approach would take O(n^2) time, but the presenter demonstrates a more efficient O(n) method using cumulative sums to minimize calculation time.

The final implementation computes values using left and right sum variables, allowing for a direct calculation of the required differences in a single pass.