Pattern 3: Prefix sums
Comes up in: DSA
This concept is being written. It gets the full five steps — explanation, predict, interview angle, practice with tests, and review cards. Here is exactly what it will cover, so you can study it elsewhere in the meantime.
What it covers
- prefix array
- range queries in O(1)
- prefix sum + hash map for "subarray sum = k"
- prefix products
- 2D prefix sums
Words you will know
What you will practise
- range-sum-query (E)
- product-except-self (M)
- subarray-sum-equals-k (M)
- contiguous-binary-array (M)
Interview questions this answers
- Find the number of subarrays whose sum is k in O(n).