Given two arrays of strings list1 and list2, find all common strings that have the minimum index sum.

A common string is a string that appears in both list1 and list2. The index sum of a common string is defined as the sum of its $0$ based index in list1 and its $0$ based index in list2.

Return a list of all common strings with the smallest index sum. You may return the answer in any order.

Constraints:

• $1 \leq$ list1.length, list2.length $\leq 1000$

• $1 \leq$ list1[i].length, list2[i].length $\leq 30$

• list1[i] and list2[i] consist of spaces ' ' and English letters.

• All strings in list1 are unique.

• All strings in list2 are unique.

• There is at least one common string between list1 and list2.

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