Find First and Last Occurrences of an Element in a Sorted Array Using Binary Search | Java DSA Guide
In this video, we tackle an important Data Structures and Algorithms (DSA) problem: Finding the First and Last Occurrences of an Element in a Sorted Array. Using Binary Search, we achieve an optimized O(log N) solution instead of a brute-force O(N) approach.
Problem Statement:
Given a sorted array with possible duplicate elements, we need to find the first and last occurrence of a given number x. If x is not found, return [-1, -1].
Example Test Case:
Input:
arr[] = [1, 3, 5, 5, 5, 5, 67, 123, 125], x = 5
Output:
[2, 5]
Explanation:
First occurrence of 5 is at index 2
Last occurrence of 5 is at index 5
Approach:
We will use two binary searches:
1️⃣ First Occurrence Search – Move left to find the first index of x.
2️⃣ Last Occurrence Search – Move right to find the last index of x.
Time Complexity Analysis:
First Occurrence: O(log N)
Last Occurrence: O(log N)
Total Complexity: O(2 * log N) ≈ O(log N)
This Java implementation ensures optimal performance compared to a naive linear search (O(N)).
Topics Covered:
✅ Binary Search Implementation
✅ Efficient Searching in Sorted Arrays
✅ Optimized Java DSA Coding Approach
✅ Handling Edge Cases in Interview Problems
📌 Whether you're preparing for FAANG interviews or enhancing your DSA skills, this problem is crucial. Watch the full explanation with detailed code walkthrough and dry run.
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