Prefix Sum Visualizer
Visualize how specific algorithm patterns work step-by-step. Build intuition for array transformations, O(1) queries, and hash map optimizations.
1D Prefix Sum Construction
Build a prefix sum array where prefix[i] stores the sum of all elements from index 0 to i-1.
def build_prefix_sum(nums):
prefix = [0] * (len(nums) + 1)
for i in range(len(nums)):
prefix[i + 1] = prefix[i] + nums[i]
return prefixMastering Prefix Sum
The Prefix Sum pattern is a fundamental technique that pre-processes an array to answer range queries in constant time. From simple 1D arrays to complex 2D matrices and difference arrays, this pattern appears frequently in coding interviews.
1D Construction
Learn how to build the cumulative sum array efficiently in a single pass.
Range Queries
Understand the query formula P[R+1] - P[L] to calculate sums in O(1).
Hash Map Opt.
Master the "Two Sum" variant for finding subarrays that sum to exactly K.
Common Interview Problems
- 01Range Sum Query - Immutable
The classic introduction to the pattern. Practice building the array and handling indices.
- 02Subarray Sum Equals K
A "must-know" problem combining prefix sums with hash maps to count subarrays.
- 03Product of Array Except Self
Uses the prefix (and suffix) concept for products instead of sums.
Learn More
Explore our comprehensive guides to master every variation:
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