无重复全排列

输入一个字符串，打印出所有排列，要求没有重复：如：输入“aab”, 输出："aab", "aba", "baa".

#include <iostream>#include <string>using namespace std;bool exchangeable(string &s, int begin, int end){    for (int i = begin; i < end; i++)    {        if (s[i] == s[end])        {            return false;        }     }    return true;}void arrange(string &s, int begin){    if (begin == s.length())    {        cout << s << endl;    }    else    {        for (int i = begin; i < s.length(); i++)        {            if (exchangeable(s, begin, i))            {                swap(s[begin], s[i]);                arrange(s, begin+1);                swap(s[begin], s[i]);            }        }    }}int main(){string a = "addd";arrange(a, 0);return 0;}