Lecture Notes: Coding Interview Questions - Two Sum Problem

Introduction

• Topic: Two Sum problem from LeetCode.
• Objective: Return indices of two numbers in an array that add up to a given target.
• Assumption: Each input array has exactly one solution; no element is used twice.
• Output Order: Indices can be returned in any order.

Problem Explanation

• Example 1:

  • Input: [2, 7, 11, 15], Target: 9
  • Output: Indices 0 and 1 because 2 + 7 = 9.

• Example 2:

  • Input: [3, 2, 4], Target: 6
  • Output: Indices 1 and 2 because 2 + 4 = 6.

Solution Strategy

• Brute Force Approach:
  • Use two nested loops.
  • First loop variable i iterates over the array.
  • Second loop variable j iterates from i + 1 to the end of the array.
  • Check if nums[i] + nums[j] == target.
  • Return the indices i and j once the pair is found.

Implementation

• Programming Language: Java.
• Data Structures:
  • Use an array to store the result indices.
  • Loop through the array to find the pair adding up to the target.
• Code Explanation:
  • Initialize int i and int j for looping.
  • Loop through i from 0 to nums.length - 1.
  • Use nested loop for j starting from i + 1 to nums.length.
  • If condition nums[i] + nums[j] == target is met:
    • Store i and j in an array arr.
    • Break the loop once the solution is found.
  • Return arr containing indices.

Code Walkthrough

• Initialization:
  • Array arr of size 2.
  • Loop through elements using variables i and j.
• Condition Check:
  • Add elements at i and j.
  • Check against the target.
• Result Storage:
  • Store indices in arr.
• Return Statement:
  • Return the indices array once condition is met.

Conclusion

• The code successfully finds the indices of numbers that sum up to a given target.
• The approach uses a brute force method with nested loops.
• Further optimization can be discussed in other sessions.

Additional Information

• Mentions ongoing Java course offering notes, quizzes, and projects.
• Opportunity for students to engage with projects and extra resources.

Next Steps

• Further LeetCode problems to be discussed in future videos.
• Viewer engagement: Comments are encouraged for suggestions on specific problems or video content.