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]. 题意:当数列中有重复数字时,求其全排列. 思路:和permutation一样.以[1,1,2]为例,以第一个1为开始,得到…