<p>You are given an array <code>arr</code> of size <code>n</code> consisting of <strong>non-empty</strong> strings.</p>

<p>Find a string array <code>answer</code> of size <code>n</code> such that:</p>

<ul>
	<li><code>answer[i]</code> is the <strong>shortest</strong> <span data-keyword="substring">substring</span> of <code>arr[i]</code> that does <strong>not</strong> occur as a substring in any other string in <code>arr</code>. If multiple such substrings exist, <code>answer[i]</code> should be the <span data-keyword="lexicographically-smaller-string">lexicographically smallest</span>. And if no such substring exists, <code>answer[i]</code> should be an empty string.</li>
</ul>

<p>Return <em>the array </em><code>answer</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr = [&quot;cab&quot;,&quot;ad&quot;,&quot;bad&quot;,&quot;c&quot;]
<strong>Output:</strong> [&quot;ab&quot;,&quot;&quot;,&quot;ba&quot;,&quot;&quot;]
<strong>Explanation:</strong> We have the following:
- For the string &quot;cab&quot;, the shortest substring that does not occur in any other string is either &quot;ca&quot; or &quot;ab&quot;, we choose the lexicographically smaller substring, which is &quot;ab&quot;.
- For the string &quot;ad&quot;, there is no substring that does not occur in any other string.
- For the string &quot;bad&quot;, the shortest substring that does not occur in any other string is &quot;ba&quot;.
- For the string &quot;c&quot;, there is no substring that does not occur in any other string.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr = [&quot;abc&quot;,&quot;bcd&quot;,&quot;abcd&quot;]
<strong>Output:</strong> [&quot;&quot;,&quot;&quot;,&quot;abcd&quot;]
<strong>Explanation:</strong> We have the following:
- For the string &quot;abc&quot;, there is no substring that does not occur in any other string.
- For the string &quot;bcd&quot;, there is no substring that does not occur in any other string.
- For the string &quot;abcd&quot;, the shortest substring that does not occur in any other string is &quot;abcd&quot;.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == arr.length</code></li>
	<li><code>2 &lt;= n &lt;= 100</code></li>
	<li><code>1 &lt;= arr[i].length &lt;= 20</code></li>
	<li><code>arr[i]</code> consists only of lowercase English letters.</li>
</ul>

class Solution:
	def shortestSubstrings(self, arr: List[str]) -> List[str]:
		# Find the length of the longest string
		max_len = len(max(arr, key=lambda s: len(s)))
		arr_len = len(arr)
		answer = [''] * arr_len

		# Visit each substring len
		for curr_substr_len in range(max_len + 1):
			substr_dict = {}

			# Visit each string
			for i, curr_str in enumerate(arr):
				# Generate all substrings of curr length
				curr_str_len = len(curr_str)
				for j in range(curr_str_len - (curr_substr_len - 1)):
					curr_substr = curr_str[j: j + curr_substr_len]
					substr_dict[curr_substr] = substr_dict.get(curr_substr, [i])
					if substr_dict[curr_substr][-1] != i: # Avoid adding the same string index twice
						substr_dict[curr_substr].append(i)

			# Add the unique substrings to the output if needed
			for substr, members in substr_dict.items():
				if len(members) > 1:
					continue

				str_i = members[0]
				if answer[str_i] == '':
					answer[str_i] = substr
				elif len(substr) < len(answer[str_i]):
					answer[str_i] = substr
				elif len(substr) == len(answer[str_i]) and substr < answer[str_i]:
					answer[str_i] = substr

		return answer
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