Given an array of unique strings words, return all valid word squares that can be constructed from words. You may return the result in any order.

A sequence of words forms a valid word square if the $k^{ ext{th}}$ row and $k^{ ext{th}}$ column read the exact same string for every valid index $k$.

Note: The same word may be used multiple times when constructing a word square.

Constraints:

• $1 \leq$ words.length $\leq 1000$

• $1 \leq$ words[i].length $\leq 4$

• All words[i] have the same length.

• words[i] consists of only lowercase English letters.

• All strings in words are unique.

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Implement your solution in the following coding playground.