Suppose Andy and Doris want to choose a restaurant for dinner, and they both have a list of favorite restaurants represented by strings.

You need to help them find out their common interest with the least list index sum. If there is a choice tie between answers, output all of them with no order requirement. You could assume there always exists an answer.

Example 1:

    Input: list1 = ["Shogun","Tapioca Express","Burger King","KFC"], list2 = ["Piatti","The Grill at Torrey Pines","Hungry Hunter Steakhouse","Shogun"]
    Output: ["Shogun"]
    Explanation: The only restaurant they both like is "Shogun".

Example 2:

    Input: list1 = ["Shogun","Tapioca Express","Burger King","KFC"], list2 = ["KFC","Shogun","Burger King"]
    Output: ["Shogun"]
    Explanation: The restaurant they both like and have the least index sum is "Shogun" with index sum 1 (0+1).

Constraints:

- `1 <= list1.length, list2.length <= 1000`
- `1 <= list1[i].length, list2[i].length <= 30`
- `list1[i]` and `list2[i]` consist of spaces `' '` and English letters.
- All the stings of `list1` are unique.
- All the stings of `list2` are unique.