Prefix-Sum

LeetCode 2391 note: pickup time is the total garbage count; each truck only drives to the last house with its type, using a prefix sum of travel

Introduction to Prefix Sum

LeetCode Problem Solving

LeetCode Problem Solving

LeetCode Problem Solving

LeetCode Problem Solving

LeetCode 3494 note: for each potion, push forward to get the last wizard’s finish time (everyone must be free), then subtract backward to get each wizard’s finish time

LeetCode 3070 note: submatrices containing the top-left corner are exactly the 2D prefix sums P[i][j]; count those <= k

LeetCode 1991 note: compute the total, maintain the left sum while scanning, and get the right sum as total - left - nums[i]

LeetCode 1732 note: the altitudes are prefix sums of gain starting from 0; take the maximum

LeetCode 1480 note: the definition of a prefix sum, adding each element to the previous running total

LeetCode 1413 note: the start value plus every prefix sum must be at least 1, so it is max(1, 1 - minimum prefix sum)