this is my solution for Parallel Letter Frequency Problem, You can find the full description of the problem in this link https://exercism.io/my/solutions/12020b7816e04e73b95de13d9814c35d, the unit test file taking from exercism.io, the problem description: Count the frequency of letters in texts using parallel computation.
To solve this problem i used Parallel.ForEach loop with partition-local variables