Word square maker

I made a word square searcher. A word square is a square grid with equal length words in each row and column such that the word in the first row is the word in the first column, the word in the second row is the word in the second column, and so on. Here's an example:

care
acid
ring
edge

It works by taking a file of words and indexing them by character and position such that I can find all the words that have a particular character at a particular position. The program will then build every possible word square that can be made from these words. It goes through all the words and tries them all as a first row/column in a word square. Each word is used as a basis for finding the rest of the words.

In the above example, the first row/column is "care". In order to find a suitable word for the second row/column, the index is used to find all the words that have a first letter equal to the first row's second letter. "acid"'s first letter is equal to "care"'s second letter, so it is a good candidate. Each one of these candidate words is used tentatively such that if it doesn't pan out then we can backtrack and try another candidate word. For the third row/column, the index is used to find all the words that have a first letter equal to the first row's third letter and a second letter equal to the second row's third letter. The intersection of these two groups of words would be all the suitable words that can be used as a third row. "ring"'s first letter is equal to "care"'s third letter and its second letter is equal to "acid"'s third letter as well, so it is a good candidate for the third row. This process keeps on going until none of the words make a word square given the first row/column. The program then moves on to another possible word in the first row/column.

You can find the program here: https://onlinegdb.com/By7XtdhpE.