Write a method that groups strings by their length. The method should return a map where keys are string lengths (Integer) and values are lists of strings with that length.

Method Signature

public static Map<Integer, List<String>> groupByLength(List<String> strings)

Examples

Example 1:

Input: ["cat", "dog", "apple", "bat"]
Output: {3: ["cat", "dog", "bat"], 5: ["apple"]}
Explanation: Strings are grouped by their length. Three strings have length 3, and one has length 5.

Example 2:

Input: ["a", "bb", "ccc"]
Output: {1: ["a"], 2: ["bb"], 3: ["ccc"]}
Explanation: Each string has a different length, so each gets its own group.

Example 3:

Input: []
Output: {}
Explanation: Empty input returns an empty map.

Example 4:

Input: null
Output: {}
Explanation: Null input returns an empty map.

Example 5:

Input: ["", "a", ""]
Output: {0: ["", ""], 1: ["a"]}
Explanation: Empty strings have length 0 and are grouped together.

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