Prefix sum
Precomputing running totals so any range sum is a subtraction, often paired with a hash map.
Solved
0/6
1Find Pivot Indexrunning sumEasy2Range Sum Query - Immutableprefix array · designEasy3Subarray Sum Equals Kprefix sum + hash mapMedium4Continuous Subarray Sumprefix sum + hash map · modular arithmeticMedium5Subarray Sums Divisible by Kprefix sum + hash map · modular arithmeticMedium6Number of Submatrices That Sum to Target2D prefix sum · prefix sum + hash mapHard