Map Sum Pairs

Problem

Implement a MapSum class with insert, and sum methods.

For the method insert, you'll be given a pair of (string, integer). The string represents the key and the integer represents the value. If the key already existed, then the original key-value pair will be overridden to the new one.

For the method sum, you'll be given a string representing the prefix, and you need to return the sum of all the pairs' value whose key starts with the prefix.

Example:
Input: insert("apple", 3), Output: Null
Input: sum("ap"), Output: 3
Input: insert("app", 2), Output: Null
Input: sum("ap"), Output: 5

Solution

HashMap Solution

class MapSum {

    Map<String, Integer> map;
    /** Initialize your data structure here. */
    public MapSum() {
        this.map = new HashMap<>();
    }

    public void insert(String key, int val) {
        map.put(key, val);
    }

    public int sum(String prefix) {
        int sum = 0;
        for (Map.Entry<String, Integer> entry : map.entrySet()) {
            if (entry.getKey().startsWith(prefix)) sum += entry.getValue();
        }
        return sum;
    }
}

Analysis

Pretty straightforward solution using HashMap