DFS水题 URAL 1152 False Mirrors

题目传送门

 /*
     题意：一个圈，每个点有怪兽，每一次射击能消灭它左右和自己，剩余的每只怪兽攻击
     搜索水题：sum记录剩余的攻击总和，tot记录承受的伤害，当伤害超过ans时，结束，算是剪枝吧
         回溯写挫了，程序死循环，跑不出来。等回溯原理搞清楚了，下次自己重写一遍:)
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <iostream>
 using namespace std;

 const int MAXN = ;
 const int INF = 0x3f3f3f3f;
 int a[MAXN];
 bool vis[MAXN];
 int n, ans;

 void DFS(int sum, int tot)
 {
     if (tot >= ans)    return ;
     if (sum == )    {ans = min (ans, tot);    return ;}

     for (int i=; i<=n; ++i)
     {
         if (!vis[i])
         {
             vis[i] = true;
             int s1 = (i == ) ? n : i - ;
             int s2 = (i == n) ?  : i + ;
             if (vis[s1])    s1 = ;
             if (vis[s2])    s2 = ;
             vis[s1] = true;    vis[s2] = true;
             sum -= a[s1];    sum -= a[s2];    sum -= a[i];

             tot += sum;
             DFS (sum, tot);
             tot -= sum;

             sum += a[s1];    sum += a[s2];    sum += a[i];
             vis[s1] = false;    vis[s2] = false;    vis[i] = false;
         }
     }
 }

 int main(void)        //URAL 1152 False Mirrors
 {
     //freopen ("N.in", "r", stdin);

     while (scanf ("%d", &n) == )
     {
         int sum = ;    a[] = ;
         for (int i=; i<=n; ++i)    {scanf ("%d", &a[i]);    sum += a[i];}
         memset (vis, false, sizeof (vis));

         ans = INF;    DFS (sum, );
         printf ("%d\n", ans);
     }

     return ;
 }