Add Longest Common Prefix solution in Java (#408)

[maitriupadhyay03-cell]

Closes #408

This PR adds a Java solution for the Longest Common Prefix problem.

Approach

• Horizontal scanning: start with the first string as prefix
• • Iteratively trim the prefix until it matches the start of each subsequent string
• • Return empty string if no common prefix exists

Complexity

• Time: O(S) where S = total characters across all strings
• • Space: O(1)

Test Cases

• ["flower", "flow", "flight"] → "fl"
• • ["dog", "racecar", "car"] → ""
• • ["abc", "abc", "abc"] → "abc"
• • Single string → returns itself
• • Empty string in array → ""

[maitriupadhyay03-cell]

Also added Kadane's Algorithm solution in Java to address issue #358.

The KadanesAlgorithm.java file implements the maximum subarray sum problem:

• Time Complexity: O(n)
• • Space Complexity: O(1)
• • Handles edge cases: all-negative arrays, single element, all-positive
• • Includes 4 test cases covering different scenarios