Summary of "Find Second Largest Element in Array | Remove duplicates from Sorted Array | Arrays Intro Video"

Summary of Video Content

The video is part of the "Strivers A to Z DSA course" and focuses on arrays, specifically addressing how to find the second largest element in an array and remove duplicates from a sorted array. The instructor emphasizes a systematic approach to problem-solving in data structures and algorithms (DSA) and provides multiple solutions to the problems discussed.

Main Ideas and Concepts

Introduction to arrays
- An array is a data structure that holds a fixed-size sequence of elements of the same data type (e.g., integers, characters).
- arrays are stored in contiguous memory locations, and the first index is 0.
- The maximum size of an array varies depending on whether it's declared locally or globally, with limits of 10^6 and 10^7 respectively.
Problem-Solving Approach
- In interviews, it's important to drive the conversation by asking clarifying questions and providing a Brute Force solution before optimizing it.
- The instructor outlines a pattern for approaching problems: Brute Force → Better Solution → Optimal Solution.
Finding the Largest Element in an Array
- Brute Force Solution: Sort the array and return the last element. Time complexity: O(n log n).
- Optimal Solution: Iterate through the array while keeping track of the largest element. Time complexity: O(n).
Finding the second largest element in an Array
- Brute Force Solution: Sort the array and check the second last element. Time complexity: O(n log n).
- Optimal Solution: Use two passes through the array:
  - First pass to find the largest.
  - Second pass to find the second largest by checking against the largest. Time complexity: O(n).
Checking if an Array is Sorted
- Iterate through the array and check if each element is greater than or equal to the previous one. Time complexity: O(n).
Removing Duplicates from a Sorted Array
- Brute Force Solution: Use a set to store unique elements, which takes O(n log n) time and O(n) space.
- Optimal Solution: Use a two-pointer technique to overwrite duplicates in place. Time complexity: O(n), space complexity: O(1).

Methodology/Instructions

Finding the Largest Element
- Initialize a variable to store the largest element.
- Loop through the array, comparing each element with the largest.
- Update the largest variable if a larger element is found.
Finding the second largest element
- First pass: Find the largest element.
- Second pass: Iterate again to find the second largest by checking against the largest.
Checking if Array is Sorted
- Start from the first element and check each element against the previous one.
- Return false if any element is smaller than the previous one.
Removing Duplicates from Sorted Array
- Initialize a pointer for the unique elements.
- Iterate through the array and whenever a new unique element is found, overwrite the next position in the array.