該問題答案如下：

#include<iostream>using namespace std;void f(string s,int k){	if(k == s.length()){		cout<<s<<endl;	}	for(int i = k; i < s.length(); i++){		char a = s[k]; s[k] = s[i]; s[i] = a;//試探		f(s,k+1);		char b = s[k]; s[k] = s[i]; s[i] = b;//回溯	}}int main(){	string s = "abc";	f(s,0);}