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ALGORITHMS

Algorithm Notebook

Classic interview problems, each worked through in plain JavaScript. Open one and hit submit to run it — the input array is shown on the page.

Binary Search

Find a key in a sorted array by halving the search space each step. Type a number and see whether it's there.

  • O(log n)
  • Divide & conquer
Run

Heap Sort

Build a max-heap, then repeatedly swap the root to the end and sift down to produce a sorted array in place.

  • O(n log n)
  • In-place
Run

Trapping Rain Water

Given an elevation map of unit-width bars, compute how much water is trapped between them after rain.

  • Two pointers
  • Arrays
Run

Repeating Numbers

Pull out every value that appears more than once in an array, without sorting it first.

  • Hashing
  • O(n)
Run

Pairwise Swap

Turn [1,2,3,4,…] into [2,1,4,3,…] by swapping adjacent pairs — including the odd-length edge case.

  • In-place
  • Edge cases
Run