Given a collection of numbers that might contain duplicates, return all possible unique permutations. For example,[1,1,2] have the following unique permutations:[1,1,2], [1,2,1], and [2,1,1]. 题解:跟Permutation差不多,只是这次会有重复的元素,如下图所示,如果只用DFS的话就会产生重复的排列: 上…