這是一道圖論模板題，用分治的策略即可輕松AC！

#include<bits/stdc++.h>
using namespace std;
string st1,st2,s1,s2;

void build(string st1,string st2)
{
	int len = st1.length();
	if (len == 0) return ;
	cout<<st2[len-1];
	int p = st1.find(st2[len-1]);
	s1 = st1.substr(0,p); s2 = st2.substr(0,p);
	build(s1,s2);
	s1 = st1.substr(p+1,len); s2 = st2.substr(p,len-1);
	build(s1,s2);
} 

int main()
{
	cin>>st1>>st2;
	int len = st1.length();
	cout<<st2[len-1];
	int p = st1.find(st2[len-1]);
	s1 = st1.substr(0,p) , s2 = st2.substr(0,p); 
	build(s1,s2);
	s1 = st1.substr(p+1,len); s2 = st2.substr(p,len-1);
	build(s1,s2);
	return 0;
}

【洛谷】P1030 求先序排列