我们知道第一个质数是 2、第二个质数是 3、第三个质数是 5……请你计算第 2020 个质数是多少？

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

378.Kth Smallest Element in a Sorted Matrix

The n-queens puzzle is the problem of placing n queens on an n_×_n chessboard such that no two queens attack each other.

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

Given a set of distinct integers, nums, return all possible subsets (the power set).

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

46. Permutations Given a collection of distinct integers, return all possible permutations.

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

The set [1,2,3,...,_n_] contains a total of n! unique permutations.