DFS POJ 3087 Shuffle'm Up

题目传送门

 /*
     题意：两块扑克牌按照顺序叠起来后，把下半部分给第一块，上半部给第二块，一直持续下去，直到叠成指定的样子
     DFS：直接模拟搜索，用map记录该字符串是否被搜过。读懂题目是关键。
 */
 /************************************************
 Author        :Running_Time
 Created Time  :2015-8-3 13:57:55
 File Name     :POJ_3087.cpp
 *************************************************/

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;

 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 5e3 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 map<string, int> cnt;
 string str;
 bool vis[MAXN][MAXN];
 int res, ct;
 int n;

 void DFS(string s, string t, int dep)   {
     if (!cnt.count (s))  cnt[s] = ++ct;
     if (!cnt.count (t)) cnt[t] = ++ct;
     if (vis[cnt[s]][cnt[t]])    return ;
     vis[cnt[s]][cnt[t]] = true;
     string tmp = "";
     for (int i=; i<n; ++i) {
         tmp += t[i];    tmp += s[i];
     }
     if (tmp == str) {
         if (res > dep)  res = dep;
         return ;
     }
     s = ""; t = "";
     for (int i=; i<n; ++i) s += tmp[i];
     for (int i=n; i<*n; ++i)   t += tmp[i];
     DFS (s, t, dep + );
 }

 int main(void)    {       //POJ 3087 Shuffle'm Up
     int T, cas = ;  scanf ("%d", &T);
     while (T--) {
         scanf ("%d", &n);
         string s, t;
         cin >> s >> t;  cin >> str;
         res = INF;  ct = ; cnt.clear ();   memset (vis, false, sizeof (vis));
         DFS (s, t, );
         printf ("%d %d\n", ++cas, res == INF ? - : res);
     }

     return ;
 }