Is Map Sum Pairs easy or hard?

Map Sum Pairs is rated Medium difficulty. The challenge comes from designing a data structure that efficiently supports prefix sum queries. Recognizing the Trie pattern and maintaining prefix aggregates is the key insight.

How to solve Map Sum Pairs in O(k)?

Use a Trie that stores prefix sums at each node. During insertion, compute the value difference from the previous key value and update every node along the path. For the sum operation, traverse the trie using the prefix and return the stored sum at the final node.

What is the best approach for Map Sum Pairs?

The Trie-based approach is the most efficient solution. Each node in the trie stores the cumulative value of all keys sharing that prefix. Both insert and sum operations run in O(k) time, where k is the key or prefix length, making it significantly faster than scanning all keys.

What data structure is used in Map Sum Pairs?

The optimal solution uses a Trie combined with a HashMap. The HashMap tracks previous key values so updates can adjust prefix sums correctly, while the Trie enables fast prefix traversal for the sum operation.

What is the time complexity of Map Sum Pairs?

Using a HashMap with prefix scanning gives O(1) insert time but O(n * k) time for each sum query. The optimized Trie solution performs both insert and sum operations in O(k) time, where k is the length of the key or prefix.

Map Sum Pairs Python or Java solution approach?

In Python or Java, implement a Trie node with a dictionary or array of children and store a running prefix sum at each node. Maintain a separate HashMap for key values to compute delta updates during insert operations.

Is Map Sum Pairs asked at Google, Amazon, or Meta?

Map Sum Pairs is a common design-style interview problem involving prefix queries and tries. Variations of prefix aggregation and trie-based data structures have appeared in interviews at companies like Google, Amazon, and Meta.

Description Solution Video 16:12

677. Map Sum Pairs

Medium57.4% acceptance3 companies

Design a map that allows you to do the following:

Maps a string key to a given value.
Returns the sum of the values that have a key with a prefix equal to a given string.

Implement the MapSum class:

MapSum() Initializes the MapSum object.
void insert(String key, int val) Inserts the key-val pair into the map. If the key already existed, the original key-value pair will be overridden to the new one.
int sum(string prefix) Returns the sum of all the pairs' value whose key starts with the prefix.

Example 1:

Input
["MapSum", "insert", "sum", "insert", "sum"]
[[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
Output
[null, null, 3, null, 5]

Explanation
MapSum mapSum = new MapSum();
mapSum.insert("apple", 3);  
mapSum.sum("ap");           // return 3 (apple = 3)
mapSum.insert("app", 2);    
mapSum.sum("ap");           // return 5 (apple + app = 3 + 2 = 5)

Constraints: