# Great Problems For Practice

[215. Kth Largest Element in an Array (Medium)](https://leetcode.com/problems/kth-largest-element-in-an-array/): Quick Select; Manually Implement Heap; API usage of `nth_element`, `make_heap`, `push_heap`, `pop_heap`

[1235. Maximum Profit in Job Scheduling (Hard)](https://leetcode.com/problems/maximum-profit-in-job-scheduling/): DP + Binary search because of sparse value (compared to continuous indexes)

[1830. Minimum Number of Operations to Make String Sorted (Hard)](https://leetcode.com/problems/minimum-number-of-operations-to-make-string-sorted/): permutation rank with duplicates

[472. Concatenated Words (Hard)](https://leetcode.com/problems/concatenated-words/): Trie + DP

## DP on Subsets OR Backtrack to Fill Buckets

* [698. Partition to K Equal Sum Subsets (Medium)](https://leetcode.com/problems/partition-to-k-equal-sum-subsets/)
* [473. Matchsticks to Square (Medium)](https://leetcode.com/problems/matchsticks-to-square/)
* [1723. Find Minimum Time to Finish All Jobs (Hard)](https://leetcode.com/problems/find-minimum-time-to-finish-all-jobs/)

## Geometry

* [478. Generate Random Point in a Circle (Medium)](https://leetcode.com/problems/generate-random-point-in-a-circle/)

## Trie + XOR

* [421. Maximum XOR of Two Numbers in an Array (Medium)](https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array/)
* [1707. Maximum XOR With an Element From Array (Hard)](https://leetcode.com/problems/maximum-xor-with-an-element-from-array/)
* [1803. Count Pairs With XOR in a Range (Hard)](https://leetcode.com/problems/count-pairs-with-xor-in-a-range/)

## BIT (Binary Index Tree) or Segment Tree

* [307. Range Sum Query - Mutable (Medium)](https://leetcode.com/problems/range-sum-query-mutable/)

## Backtracking

* [51. N-Queens (Hard)](https://leetcode.com/problems/n-queens/)
* [698. Partition to K Equal Sum Subsets (Medium)](https://leetcode.com/problems/partition-to-k-equal-sum-subsets/)
* [473. Matchsticks to Square (Medium)](https://leetcode.com/problems/matchsticks-to-square/)

## Stack operation on string

* [1003. Check If Word Is Valid After Substitutions (Medium)](https://leetcode.com/problems/check-if-word-is-valid-after-substitutions/)
* [1209. Remove All Adjacent Duplicates in String II (Medium)](https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/)

## Permutation

* [60. Permutation Sequence (Hard)](https://leetcode.com/problems/permutation-sequence/)
* [31. Next Permutation (Medium)](https://leetcode.com/problems/next-permutation/)

## Mono Stack / Mono Deque

* [907. Sum of Subarray Minimums (Medium)](https://leetcode.com/problems/sum-of-subarray-minimums/)

## Sorting

* [912. Sort an Array (Medium)](https://leetcode.com/problems/sort-an-array/)

## Binary Indexed Tree

* [307. Range Sum Query - Mutable (Medium)](https://leetcode.com/problems/range-sum-query-mutable)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://liuzhenglaichn.gitbook.io/algorithm/great-problems-for-practice.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.