You are given an array of non-negative integers. A pair of indices (i, j) is nice if nums[i] + rev(nums[j]) equals nums[j] + rev(nums[i]). Return the number of nice pairs modulo 10^9 + 7.
Given a string sentence consisting of lowercase English letters, determine whether the sentence contains every letter of the English alphabet at least once.
You are given two integer arrays nums1 and nums2. Your task is to implement a data structure that supports two types of operations: 1) Add a value to an element in nums2. 2) Count the number of pairs (i, j) such that nums1[i] + nums2[j] equals a given total value.
You are given a string s, and your task is to find the number of substrings of length 3 that contain no repeated characters. A substring is considered ‘good’ if all its characters are unique. Note that if a ‘good’ substring appears more than once, it should be counted multiple times.
You are given a list of integer ranges and two integers, left and right. Each range is represented by a pair of integers [start, end]. You need to determine if all integers from left to right (inclusive) are covered by at least one of these ranges. An integer x is considered covered by a range [start, end] if start <= x <= end.