Given two strings s and t, determine if they are isomorphic.

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

Given an array of integers nums, calculate the pivot index of this array.

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.