array-problems.md

Array

• ✅ Problem listing: https://leetcode.cn/circle/discuss/E3yavq/#%E6%8E%92%E5%BA%8F%E7%AE%97%E6%B3%95%E7%AF%87
• ✅ https://huxulm.github.io/lc-rating/list/data_structure 常用枚举技巧
• ✅ TODO: Practice https://blog.faangshui.com/p/before-leetcode
• TODO: Understand how to iterate in diagonal, see Code Template

Enumeration

枚舉右，維護左

Problem	Difficulty	Note
1512. Number of Good Pairs	Easy	Count frequency of seen.
1679. Max Number of K-Sum Pairs	Medium (1345)	Variant of 1. Two Sum
**1010. Pairs of Songs With Total Durations Divisible by 60	Medium (1377)	Pair 60 - (t % 60) or t % 60 == 0.
219. Contains Duplicate II	Easy	Sliding window [i - k, i].
**624. Maximum Distance in Arrays	Medium	Prefix max/min from opposite ends.
**1031. Maximum Sum of Two Non-Overlapping Subarrays	Medium (1680)	[First,Second] or [Second,First] + prefix sum.
1014. Best Sightseeing Pair	Medium (1730)	Seen values[i] + i, enumerate values[j] - j.
1814. Count Nice Pairs in an Array	Medium (1737)	Seen A - rev(A), enumerate B - rev(B).

枚舉中間

Problem	Difficulty	Note
238. Product of Array Except Self	Medium	Prefix / suffix product.
2909. Minimum Sum of Mountain Triplets II	Medium (1478)	Fix middle, trakc min lefet and right.
2874. Maximum Value of an Ordered Triplet II	Medium (1583)	Prefix max, maxDiff.

Movement

Problem	Difficulty
283. Move Zeroes	Easy
189. Rotate Array	Medium
665. Non-decreasing Array	Medium

Iteration

Problem	Difficulty

• https://leetcode.com/problems/teemo-attacking/description/ e
• https://leetcode.com/problems/third-maximum-number/description/ e
• https://leetcode.com/problems/maximum-product-of-three-numbers/description/ e

2D Array

Problem	Difficulty

• https://leetcode.com/problems/pascals-triangle/description/ e
• https://leetcode.com/problems/pascals-triangle-ii/ e
• https://leetcode.com/problems/reshape-the-matrix/description/ e
• https://leetcode.com/problems/image-smoother/description/ e
• https://leetcode.com/problems/battleships-in-a-board/description/ m
• https://leetcode.com/problems/game-of-life/description/ m
• https://leetcode.com/problems/diagonal-traverse/description/

To Classify

Problem	Difficulty	Note
989. Add to Array-Form of Integer	Easy	Simulation.
334. Increasing Triplet Subsequence	Medium	Mind the check order of first and second.
581. Shortest Unsorted Continuous Subarray	Medium	Prefix max + suffix min.
941. Valid Mountain Array	Easy
845. Longest Mountain in Array	Medium
73. Set Matrix Zeroes	Medium	Use first row and column as markers
766. Toeplitz Matrix	Easy
48. Rotate Image	Medium
54. Spiral Matrix	Medium
59. Spiral Matrix II	Medium
189. Rotate Array	Medium
136. Single Number	Easy
31. Next Permutation	Medium

Sorting

Problem	Difficulty
912. Sort an Array	Medium
75. Sort Colors	Medium
148. Sort List	Medium

Solved: https://leetcode.com/problems/height-checker/