ARRAY PRACTICE PROBLEMS | Must do Array Questions | DSA Problems | GeeksforGeeks

Summary

In this video, the presenter discusses the top 5 array-related interview questions, focusing on key algorithms and problem-solving techniques. Each question introduces new concepts like finding leaders in an array, sorting arrays of 0s, 1s, and 2s using the Dutch national flag algorithm, and counting elements occurring more than n/k times. Additionally, viewers learn about Kadane’s algorithm for finding the maximum subarray sum and the smallest positive missing number using the bucketing technique. The presenter encourages viewers to try solving these questions on their own and share solutions.

Takeaways

• 😀 The video covers the top 5 interview questions on arrays, each chosen to teach new algorithms and concepts.
• 💡 The first question is about finding 'leaders' in an array. A leader is an element greater than or equal to all elements on its right.
• 🔎 To solve the 'leaders' question, traverse the array from right to left, track the maximum, and update it when necessary.
• 📊 The second question is about sorting an array of 0s, 1s, and 2s. A faster solution using the Dutch National Flag algorithm is recommended.
• 📈 The third question asks for elements with a frequency greater than n/k in the array, solvable with Moore's Voting Algorithm.
• 🔧 The fourth question involves Kadane's Algorithm, which finds the contiguous subarray with the maximum sum.
• 🔢 The fifth question asks for the smallest positive missing number in an array. A bucketing technique can optimize the solution.
• 💭 Each question teaches useful variations or optimizations on common array problems for interview preparation.
• 🚀 For the second question, instead of traditional sorting, partition the array into sections of 0s, 1s, and 2s using pointers.
• 🧠 The video encourages viewers to attempt solving the problems on their own before looking up the algorithms.

Q & A

What is the definition of a leader in an array?

A leader in an array is an element that is greater than or equal to all the elements to its right. For example, in an array, if no element on the right side of a number is greater than or equal to it, that number is considered a leader.

How can you find the leaders in an array?

To find the leaders, you can start traversing the array from right to left. Keep track of a 'maximum' variable initialized to the last element of the array, which is always a leader. As you move left, update the 'maximum' if you encounter a number greater than the current 'maximum' and add it to the list of leaders.

What algorithm is recommended for sorting an array of 0s, 1s, and 2s in O(n) time?

The Dutch National Flag algorithm is recommended for sorting an array of 0s, 1s, and 2s in O(n) time. It works by dividing the array into three partitions: one for 0s, one for 1s, and one for 2s, and then sorting the elements using pointers.

What is the task in the 'Count more than n by k occurrences' problem?

The task is to find all the elements in an array whose frequency is greater than n divided by k, where n is the size of the array and k is a given number.

What algorithm can be used to solve the 'Count more than n by k occurrences' problem?

The Moore's Voting Algorithm can be used to solve the 'Count more than n by k occurrences' problem. It efficiently finds the elements that occur more than n/k times by iterating through the array and counting element frequencies.

What is the goal of Kadane's algorithm?

Kadane's algorithm aims to find the contiguous subarray within a one-dimensional array that has the maximum sum. It is commonly used to solve problems where you need to find the subarray with the maximum sum in O(n) time.

How does Kadane's algorithm work?

Kadane's algorithm works by iterating through the array and keeping track of the current subarray sum and the maximum sum encountered so far. If the current sum becomes negative, it resets to zero, as any further elements will reduce the total sum.

What is the 'Smallest positive missing number' problem about?

The 'Smallest positive missing number' problem requires you to find the smallest positive integer that is missing from a given array of integers. The array may include negative numbers and zero.

What optimization technique can be used to solve the 'Smallest positive missing number' problem?

The bucketing technique can be used to solve the problem in O(n) time. This involves marking the presence of elements within the array by using their index positions, so you don't need extra space and can identify the missing number quickly.

What are some common variations of the 'Count more than n by k occurrences' problem?

Some common variations include finding elements that occur more than n/2 times or more than n/3 times. These variations can appear in interviews, where different values of k are provided, and the problem is redefined based on the division of n by k.