Master LeetCode Patterns

3 Problems

Fenwick Tree (BIT) Practice Problems

Dynamic prefix sums/frequencies and order statistics using a Binary Indexed Tree.

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Relevant Patterns

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Fenwick Tree (Binary Indexed Tree)Range Queries

Practice Problems

1

Count of Smaller Numbers After Self

Hard#315

Show 2 hints

Process from right; query prefix counts of values < current.
Coordinate compress values to 1..m.

2

Hard#493

Show 2 hints

Count pairs (i<j, nums[i] > 2*nums[j]) via BIT over compressed values.
Alternatively use mergesort counting.

3

Create Sorted Array through Instructions

Hard#1649

Show 2 hints

Cost is min(count < x, count > x); maintain BIT of frequencies.
Use modulo arithmetic as required by problem.

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