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divide and conquer
dfs/bfs
Dependency related problems
- union find
- keep track of a set of elements with degree of 0, until the set is empty
Think from end state and reverse to start state (e.g. remove -> add)
Two player game, each player tries out all possible moves, in order to find maximum or minimum result depends on which side the player is.
Sometimes we can extend the string by duplicating it or add a reversed version to the end.
Typical toplogical sort
- Get all items
- Create indegree and outdegree maps
- Find 0 outdegree items
- Iteratively update the outdegree map by referring to indegree map and insert new free items
knapsack problem or set cover problem, use dp for all problem space
Great article about range problems
- https://leetcode.com/problems/reverse-pairs/discuss/97268/General-principles-behind-problems-similar-to-%22Reverse-Pairs%22
Solve rectangle problem by counting number of lines
Convert array into increasing array using deque by poping out elements >= incoming element
Bit operations
- Negative number is get the opposite then + 1
- i & -1 keeps last 1 bit
Two ways to partition
- One: result will have elements < condition first, >= condition rest. For duplicates, it will either contain all duplicates or none, such as 1 ~ 2 2 2 3. We'll need another partition that have element <= condition first, > condition reset. e.g. 1 2 2 2 ~ 3 in order to sort or find kth.
- Two: result will have elements <= conditions first, >= conditions rest, such as 2 1 1 ~ 2 2, so that first k elements will be the k elements if sorted

Name		Name	Last commit message	Last commit date
Latest commit History 846 Commits
cmake_test		cmake_test
leetcode		leetcode
.gitignore		.gitignore
CommonTicks.txt		CommonTicks.txt
README.md		README.md
avltree.cpp		avltree.cpp
binaryIndexedTree.cpp		binaryIndexedTree.cpp
bit_check.cpp		bit_check.cpp
dijkstra.cpp		dijkstra.cpp
heapsort.cpp		heapsort.cpp
kmp.cpp		kmp.cpp
monoqueue.cpp		monoqueue.cpp
quicksort.cpp		quicksort.cpp
reverset_linked_list.cpp		reverset_linked_list.cpp
singleton.cpp		singleton.cpp
trie.cpp		trie.cpp
unionfind.cpp		unionfind.cpp

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