# Halo

A magic place for coding

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## beta-recsys v0.1 版本发布啦！🎉🎉🎉

我们的 beta-recsys v0. 1 版本发布了！这是一个基于 pytorch 的推荐系统来源平台，我们致力于整合更多的推荐系统模型，为推荐系统这个社区提供一个公平比较的平台，同时推进代码的可复现性！
Github: https://github.com/beta-team/beta-recsys

**teaser video:**https://vimeo.com/456391232

## Problem

Given the root of a binary tree, return the sum of values of its deepest leaves.

## Problem

Given an m x n integers matrix, return the length of the longest increasing path in matrix.

From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary (i.e., wrap-around is not allowed).

## Problem

In an alien language, surprisingly they also use english lowercase letters, but possibly in a different order. The order of the alphabet is some permutation of lowercase letters.

Given a sequence of words written in the alien language, and the order of the alphabet, return true if and only if the given words are sorted lexicographicaly in this alien language.

## Problem

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

## Problem

You are given a string s of even length. Split this string into two halves of equal lengths, and let a be the first half and b be the second half.

Two strings are alike if they have the same number of vowels ('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'). Notice that s contains uppercase and lowercase letters.

Return true if a and b are alike. Otherwise, return false.

## Problem

You have an array arr of length n where arr [i] = (2 * i) + 1 for all valid values of i (i.e. 0 <= i < n).

In one operation, you can select two indices x and y where 0 <= x, y < n and subtract 1 from arr [x] and add 1 to arr [y] (i.e. perform arr [x] -=1and arr [y] += 1). The goal is to make all the elements of the array equal. It is guaranteed that all the elements of the array can be made equal using some operations.

Given an integer n, the length of the array. Return the minimum number of operations needed to make all the elements of arr equal.

## Problem

You are given an integer array nums of length n which represents a permutation of all the integers in the range [0, n - 1].

The number of global inversions is the number of the different pairs (i, j) where:

• 0 <= i < j < n
• nums [i] > nums [j]

The number of local inversions is the number of indices i where:

• 0 <= i < n - 1
• nums [i] > nums [i + 1]

Return true if the number of global inversions is equal to the number of local inversions.