Dutch National Flag Algorithm in Java | Sort 0s, 1s, 2s Without Sorting | Two Pointer Approach
In this Java tutorial, we implement the Dutch National Flag Algorithm, an efficient in-place sorting technique to sort an array consisting only of 0s, 1s, and 2s. This is a classic array-based interview problem frequently asked in coding rounds at top tech companies like Google, Amazon, and Microsoft.
✅ Problem Statement:
Given an array of integers containing only 0, 1, and 2, sort it in a single traversal using constant space without using any built-in sorting algorithms.
✅ Algorithm Used:
We solve this using the Two-Pointer Approach, also known as the Dutch National Flag problem, originally proposed by Edsger Dijkstra.
✅ Key Concepts Covered:
How to use low, mid, and high pointers
In-place sorting logic
Time Complexity: O(n)
Space Complexity: O(1)
Step-by-step dry run and visualization
✅ Example Used in Code:
Input: [0,1,2,0,1,1,1,0,2,0,2,1]
Output: [0,0,0,0,1,1,1,1,1,2,2,2]
✅ Code Implementation:
Java code is written from scratch with clear explanation, comments, and visual debugging. Mistakes during the live session are also shown (with fun text pop-ups!) to simulate real coding sessions and help you learn better.
🎯 Perfect For:
Beginners learning Java
Students preparing for data structures and algorithms
Anyone practicing for coding interviews
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