Given an array of integers nums and a target integer target, find and return the indices of two distinct numbers in the array that sum up to the given target. The solution is guaranteed to exist for the given input. You can return the indices in any order.
Given a string, determine the length of the longest substring that contains no repeating characters. The substring must consist of consecutive characters, and its length is to be returned as the output.
You are given a positive integer and need to convert it into a Roman numeral. Roman numerals are constructed by combining symbols from the set: I, V, X, L, C, D, M, where each symbol has a specific value. The conversion rules are based on subtractive notation for values like 4 (IV), 9 (IX), and so on, to avoid using symbols multiple times where not allowed.
Determine if a 9x9 Sudoku board is valid. A valid Sudoku board follows three rules: Each row, column, and 3x3 sub-box must contain the digits 1-9 without repetition. Only the filled cells need to be validated.
