Two Pointers Algorithm Visualizer
Interactive tool to master Two Pointers techniques for coding interviews. Visualize opposite direction, palindrome checking, and in-place array manipulation algorithms step-by-step.
Two Sum II (Sorted)
Find two numbers in a sorted array that add up to a specific target.
def two_sum(numbers, target):
left, right = 0, len(numbers) - 1
while left < right:
curr_sum = numbers[left] + numbers[right]
if curr_sum == target:
return [left + 1, right + 1]
elif curr_sum < target:
left += 1
else:
right -= 1
return []Understanding Two Pointers Patterns
The Two Pointers technique reduces time complexity from O(N²) to O(N) by using two indices to traverse the data structure. Instead of nested loops, we make intelligent decisions at each step to eliminate impossible solutions or manipulate data in-place.
Core Patterns Visualized
Opposite Direction
Pointers start at opposite ends and move inward. Used for sorted arrays (Two Sum) and palindromes.
Read & Write (In-Place)
Pointers move in the same direction. One reads elements, the other writes valid ones. Ideal for removing elements or partitioning.
Fast & Slow
Used primarily for linked lists (Cycle Detection) or sliding windows, moving at different speeds.
Key Insight
The efficiency comes from monotonicity: in a sorted array, moving the left pointer right always increases the sum, and moving the right pointer left always decreases it. This allows us to make O(1) decisions at each step.
How to Use the Visualizer
- Select a problem type (Two Sum, Palindrome, Move Zeroes)
- Use Next/Previous buttons to step through the algorithm logic
- Watch the pointers (L/R or Read/Write) move and update
- Observe variable states like current sum or comparison results
- Use Auto Play to watch the algorithm run smoothly
Practice Problems
Apply what you've learned with these classic LeetCode problems:
Learn More
Explore our comprehensive Two Pointers guides:
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