599 Minimum Index Sum of Two Lists

Intuition

We can store all the words from the first list into a hashtable along with their indices as the keys. Then iterate over the other list, and the word in list2 is already seen in the list1 - then calculate the current index_sum with indices[i] + i.

If the current index_sum is lower than previous than create a new result list, else if the sum is equal to current lowest, append the word to the result list.

Code

Python3

def findRestaurant(self, list1: List[str], list2: List[str]) -> List[str]:
 
    indices = defaultdict(int)
 
    for i, word in enumerate(list1):
        indices[word] = i
 
 
    result = []
    least_sum = float('inf')
 
    for i, word in enumerate(list2):
        if word in indices:
            index_sum = indices[word] + i
 
            if index_sum < least_sum:
                result = [word]
                least_sum = index_sum
            elif index_sum == least_sum:
                result.append(word)
 
    return result

Big O Analysis

• Runtime

  The runtime complexity here is $O(N)$ where N is the max of lengths of list1 and list2.

• Memory

  The memory usage is $O(N)$ since use a hashtable to store words and their corresponding indices.

— A

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