摘要：
Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. For example, If n = 4 and k = 2, a solution is: 做了好几个这种题了，就是 阅读全文
摘要：
Given a collection of numbers that might contain duplicates, return all possible unique permutations. For example, have the following unique permutati 阅读全文