"ab"
["ab","ba"]
返回["ba","ab"]也是正确的
"aab"
["aab","aba","baa"]
"abc"
["abc","acb","bac","bca","cab","cba"]
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解题思路：
本题的思路和之前回溯的思想一样，不过更简单的做法是将字符串的每个字符先进行排序，再进行回溯，这样可以方便去除重复的字符串；去重这一部分我还没完全搞懂。。。所以还得多练
原文：https://www.cnblogs.com/hddandelion/p/15172903.html