LeetCode #599 Minimum Index Sum of Two Lists

Easy

Problem

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.

Solution

Use a hash map to store indices of restaurants in list1 and iterate list2 to get the one which has least index sum.

Complexity

Assume m and n denote to counts of restaurants of list1 and list2. It takes O(m) time to build the hash map. And then it takes O(n)/O(nlogm) time in average/worst cases to iterate list2 and check if elements are in list1. Therefore, its time complexity is O(m + n)/O(m + nlogm) in average/worst cases.

It needs O(m) extra space to maintain the hash map.