SPELLING CHECKER DATA STRUCTURE DESCRIPTIONS
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The dictionary is a set of words.
It will be searched once for each word in the document,
so the search operation must be very fast.
My program will store the dictionary words in a hash table.
This is a good choice because hash tables provide very fast
searching, and there is no need to store the dictionary words
in sorted order.

The error report is a map that associates each misspelled word 
with a list of line numbers where the word appears in the document.
The spelling checker will search the error report once for
each word in the document, so searching the error report for a 
particular word must be very fast.
It is also necessary to store the misspelled words in sorted order.
My program will store the error report in a balanced binary search
tree, which will provide both sorting and efficient searching.