记录贴，互勉

207. Course Schedule
Check indegree of each course

微信用户_b99d1cc 发表于 2023-9-20 10:52
207. Course Schedule
Check indegree of each course

可以对Queue里面的for loop优化，通过arrayList记住需要cur作为pre对应的课，只访问对应的课而不是所有的pair

210. Course Schedule II
Topological order

802. Find Eventual Safe States
Graph coloring:    1 if visited, 2 if terminal, 0 if unvisited
DFS solution

399. Evaluate Division
UnionFind solution
a/b = 2 which means a=2b we can set b as root, weight[a] = 2
In order to use unionFind, we need to map the String value to an index.

839. Similar String Groups
UnionFind, uses a function to check if the string is similar to another string.

905. Sort Array By Parity
use front counter and end counter to put the even and odd from the beginning and end of the array

952. Largest Component Size by Common Factor
Use union-find to union all the factors of the number, then find the largest common factor by map the root and count of each number.
Key point: for each number, the largest factor number is less than sqrt(num).

990. Satisfiability of Equality Equations
union-find solution:
Union the == character.   
Compare the != root

721. Accounts Merge
1. map email to id
2. If the same email maps to a different id, union these two ids
3. put the email together with the root Id
4. sort the email and put them to an array, add the account name to the top.