This content originally appeared on DEV Community and was authored by Mohammed mhanna
Ever spent hours writing nested loops to solve simple array or string problems, only to feel it’s slow and messy?
The Two Pointer Technique is a game-changer. It’s a powerful strategy to traverse arrays, lists, or strings efficiently using two markers (pointers), reducing time complexity and improving code readability.
By the end of this post, you’ll know:
What the Two Pointer Technique is
How it works step by step
Real-world examples in Java
Common pitfalls to avoid
Practice challenges to master it
🌱 What Is the Two Pointer Technique?
The Two Pointer Technique uses two indices to iterate over data structures:
Opposite ends: One pointer at the start, one at the end
Same start: Slow and fast pointers moving at different speeds
✅ Ideal for sorted arrays, strings, and problems that require comparison or condition checking.
🛠 How It Works: Step by Step
1️⃣ Opposite Ends
Move pointers toward each other based on conditions.
Common for: finding pairs with a target sum, checking palindromes.
2️⃣ Same End (Slow & Fast)
Slow pointer moves step by step
Fast pointer moves faster
Detect duplicates, cycles in lists, or sliding window problems
3️⃣ Adjust Pointers Dynamically
If current condition < target → move left/slow forward
If current condition > target → move right/fast backward
Stop when pointers meet or satisfy problem condition
💡 Examples in Java
Example 1: Reverse an Array
int left = 0, right = arr.length - 1;
while(left < right){
int temp = arr[left];
arr[left] = arr[right];
arr[right] = temp;
left++; right--;
}
✅ Enforcement: In-place reversal saves memory and time.
Example 2: Pair With Target Sum
int left = 0, right = arr.length - 1;
while(left < right){
int sum = arr[left] + arr[right];
if(sum == target){ System.out.println(arr[left] + ", " + arr[right]); break; }
else if(sum < target) left++; else right--;
}
✅ Enforcement: Linear time solution instead of nested loops.
Example 3: Remove Duplicates from Sorted Array
int i = 0;
for(int j = 1; j < arr.length; j++){
if(arr[j] != arr[i]){
i++;
arr[i] = arr[j];
}
}
✅ Enforcement: In-place modification reduces memory usage.
🌍 Real-World Applications
Palindrome check in strings
Two-sum problems in finance, scoring apps
Sliding window problems: max/min in a range
Cycle detection in linked lists
⚠️ Common Pitfalls & Mistakes
❌ Using Two Pointers on unsorted arrays without sorting first
❌ Moving pointers incorrectly → infinite loops or missed elements
❌ Using nested loops when two pointers suffice
❌ Ignoring boundary conditions (array length, empty arrays)
✅ Tip: Always visualize the pointer movement before coding.
🧩 Practice Challenges
Check if a string is a palindrome using two pointers.
Merge two sorted arrays efficiently.
Find all triplets in an array with a given sum.
Detect a cycle in a linked list (slow & fast pointers).
Sliding window: Find max sum of size k subarrays.
📚 Resources to Level Up
GeeksforGeeks: Two Pointer Technique
LeetCode: Two Pointer Problems
🎯 Takeaway
The Two Pointer Technique is your secret weapon for solving array and string problems efficiently. It improves performance, reduces complexity, and makes your code cleaner and more readable.
💬 Engagement Questions:
Which problem did two pointers help you solve the most?
Can you think of a scenario where this technique would save time in your project?
Have you tried slow & fast pointers for linked lists yet?
Drop your thoughts in the comments — let’s discuss and learn together! 🚀
This content originally appeared on DEV Community and was authored by Mohammed mhanna
Mohammed mhanna | Sciencx (2025-09-20T15:11:10+00:00) ⚡ Two Pointer Technique. Retrieved from https://www.scien.cx/2025/09/20/%e2%9a%a1-two-pointer-technique/
Please log in to upload a file.
There are no updates yet.
Click the Upload button above to add an update.