# 599 Minimum Index Sum of Two Lists

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:

["Shogun", "Tapioca Express", "Burger King", "KFC"]
["Piatti", "The Grill at Torrey Pines", "Hungry Hunter Steakhouse", "Shogun"]

Output:
 ["Shogun"]

Explanation:
 The only restaurant they both like is "Shogun".
```

**Example 2:**

```
Input:

["Shogun", "Tapioca Express", "Burger King", "KFC"]
["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).
```

**Note:**

1. The length of both lists will be in the range of \[1, 1000].
2. The length of strings in both lists will be in the range of \[1, 30].
3. The index is starting from 0 to the list length minus 1.
4. No duplicates in both lists.

**The Idea:** Aggregate the the sum of indices that share common interests into a list. Then all the remains will be to return the appropriate list that is mapped from the lowest sum of indices.

**Complexity:** O(n) time and space

```python
import collections


class Solution:
    def findRestaurant(self, list1, list2):
        """
        :type list1: List[str]
        :type list2: List[str]
        :rtype: List[str]
        """

        fav2 = {word:i for i, word in enumerate(list2)}
        ties_dictionary = collections.defaultdict(list)

        for i, restaurant in enumerate(list1):
            if restaurant in fav2:
                ties_dictionary[fav2[restaurant]+i].append(restaurant)

        return min(ties_dictionary.items(), key=lambda x: x[0])[1]
```