You are given a list of preferences for n friends, where n is always even. Each person has a list of friends they prefer, and these friends are represented by integers from 0 to n-1. The friends are divided into pairs, where each pair is denoted by a list [xi, yi], meaning xi is paired with yi and yi with xi. However, some of the pairings may cause unhappiness. A person is unhappy if they prefer someone who is paired with someone else, and that person also prefers them over their current partner. Your task is to return the number of unhappy friends.
You are given a list of points on a 2D plane, represented as coordinates [x, y]. The cost of connecting two points is defined by the Manhattan distance, which is calculated as |xi - xj| + |yi - yj|. Your task is to return the minimum total cost required to connect all the points. A valid connection between points must form a connected graph, where there is exactly one simple path between any two points.
You are given an array of integers nums and a list of requests, where each request specifies a range in the array. The ith request asks for the sum of all elements from nums[starti] to nums[endi], inclusive. Your task is to determine the maximum total sum of all requests for any permutation of nums.
Given an array of positive integers nums and an integer p, your task is to remove the smallest subarray (contiguous elements) such that the sum of the remaining elements is divisible by p. If it’s impossible, return -1. Note that the entire array cannot be removed.
Given a string s, your task is to split it into the maximum number of non-empty substrings such that all substrings are unique. You are allowed to split the string in any way, but each substring in the split must not repeat.
You are given a m x n matrix grid. Starting at the top-left corner (0, 0), you can only move right or down. Your task is to find the path from the top-left to the bottom-right corner that results in the maximum non-negative product of the grid values along the path. If such a path results in a negative product, return -1. The product is calculated by multiplying all grid values visited along the path. You should return the maximum non-negative product modulo 10^9 + 7.