Frequently used algorithms in Leetcode

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本文深入探讨了算法和数据结构的关键概念，包括二叉树、队列、栈、数组、链表等基本数据结构，以及二分搜索、树遍历、图论等算法策略。此外，还详细介绍了排序算法、动态规划、哈希算法、贪心算法等高级算法，旨在为读者提供全面的计算机科学基础知识。

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1. Bianry search:

(1) Sorted array, but not linked-list. BS requires backtracking.Double linked-list is also not a good data structure! BS also requires randomly access every elements. Double linked-list must access each element from last (either left or right), and then this decrease the time complexity from logn to n.

(2) Two pointer: start and end. The key point of such problems is how to design the condition that jump out of the loop (start < end or start <= end). In this point, we should consider corner cases.

(3) Another point that may cause failure is that the middle index may equal to start (when start == end - 1). This may cause endless loop.

(4) A speed up way is to move index (new start or end) to the next different entry. (Ref: 3 sum)

2. Tree traversals:

(1) Recursive or non-recursive: recursive does not mean to slower than non-recursive.

(2) BFS or DFS.

(3) Pre-order, In-order or Post-order. The key to solve problems is to choose a proper method. (Post-order is better/must for recurse every pathes)

3. Graph.

4. Math:

4.1 Overflow: Use unsigned int or long long to take the number need to calculate.

4.2

5. String

6. Stack and Queue.