LeetCode 2631: Group By Solution

Problem Explanation

Explanation:

To implement the groupBy method on an array, we can iterate over the array, apply the provided fn function to each element to get the key, and then group the elements based on these keys. We can use a HashMap (or dictionary in Python) to store the grouped elements. If an element with the same key already exists in the map, we append the current element to the list of values corresponding to that key.

Time complexity: O(n), where n is the number of elements in the input array.
Space complexity: O(n) to store the grouped elements in the map.

Solution Code

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ArrayGroupBy {
    public static Map<String, List<Object>> groupBy(Object[] array, Function<Object, String> fn) {
        Map<String, List<Object>> groupedMap = new HashMap<>();
        
        for (Object item : array) {
            String key = fn.apply(item);
            groupedMap.putIfAbsent(key, new ArrayList<>());
            groupedMap.get(key).add(item);
        }
        
        return groupedMap;
    }
}

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2631. Group By