How do I count the letters per word of a string array:

Example:

Given an array of type:

String[] sentence = new String[5]

With this sentence in it:

There is a cat somewhere

would return:

an array of type:

int [] wordlenghts = new int[5]

"5, 2, 1, 3, 9" // word lengths per word

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and how about if I wanted to pick only the words which contain letter "a"

so this time I would have the program return

string [] wordswitha = new string[number of words with the letter a in it]

"a, cat"

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is there a more advanced string manipulation library for these types
of processes...

obviously I am a newbie :) I will appreciate your help and guidance