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Prefix Sums

3 practice problemsInteractive visual guide

Prefix Sums let you query subarray sums quickly after one pass.

Key Ideas

  • Build pref[i] = sum of first i elements.
  • Subarray sum [l..r] is pref[r+1] - pref[l].
  • Hash map of prefix sums helps count subarrays with a target sum.

Practice Problems

Range Sum Query - Immutable

LeetCodeEasy

LeetCode: https://leetcode.com/problems/range-sum-query-immutable/

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Subarray Sum Equals K

LeetCodeMedium

LeetCode: https://leetcode.com/problems/subarray-sum-equals-k/

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Find Pivot Index

LeetCodeEasy

LeetCode: https://leetcode.com/problems/find-pivot-index/

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