I solved the 'Add Two Numbers' problem, which involves adding two numbers represented by linked lists.
I solved the 'Two Sum' problem, which requires finding two numbers in an array that sum up to a target value.
I tackled the 'Reverse Integer' problem, which requires reversing the digits of an integer.
I solved the 'Longest Substring Without Repeating Characters' problem, which requires finding the length of the longest substring without repeating characters.
I solved the 'Longest Palindromic Substring' problem, which involves finding the longest palindromic substring within a string.