Algorithm Atlas

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Learn Arrays with visual DSA lessons

Learn Arrays with 4 DSA patterns and 25 visual lessons. Follow step-by-step animations and synced C#, Python, and Java code.

An array is a row of values. Every value has a numbered place.

Two Pointers

Use two markers that move through the array.

Move Zeroes Easy · Read and write markers
Two Sum II Medium · Opposite ends
3Sum Medium · One fixed + two moving
Sort Colors Medium · Three moving markers
Container With Most Water Medium · Move the shorter side
Trapping Rain Water Hard · Two sides remember their tallest wall

Sliding Window

Keep a moving group of nearby values.

Maximum Sum Subarray of Size K Easy · Fixed-size window
Max Consecutive Ones Easy · Resetting window
Max Consecutive Ones III Medium · Grow and shrink
Subarray Product Less Than K Medium · Product window
Fruits Into Baskets Medium · At most two kinds
Minimum Size Subarray Sum Medium · Smallest valid window
Sliding Window Maximum Hard · Best value in every window
Subarray With K Distinct Integers Hard · Exactly K kinds

Prefix Sum

Save running totals so later questions become quick.

Find Pivot Index Easy · Left total equals right total
Subarray Sum Equals K Medium · Saved total + lookup
Matrix Block Sum Medium · Two-dimensional saved totals
Product of Array Except Self Medium · Left product + right product
Continuous Subarray Sum Medium · Repeated remainder
Subarray Sum Divisible by K Medium · Count matching remainders

Kadane’s Algorithm

Keep the best connected part seen so far.

Maximum Subarray Medium · Keep or restart
Maximum Product Subarray Medium · Keep or restart
Maximum Sum Circular Subarray Medium · Keep or restart
Maximum Absolute Sum of Any Subarray Medium · Keep or restart
Largest Sum Contiguous Subarray Medium · Keep or restart