枚举子集

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

Given two integers n and k, return all possible combinations of k numbers out of 1 … n. 思路：就是枚举子集，根据集合的大小剪枝。。。最后只要集合大小为k的集合

* Total Accepted: **106670** * Total Submissions: **329718** * Difficulty: **Medium** * Contributor: **LeetCode** Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Given a collection of integers that might contain duplicates, nums, return all possible subsets. Note: The solution set must not contain duplicate subsets. For example, If nums = [1,2,2], a solution is: