题目传送门
1 /*
2 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
3 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
4 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:)
5 */
6 #include <cstdio>
7 #include <algorithm>
8 #include <cstring>
9 #include <cmath>
10 #include <iostream>
11 using namespace std;
12
13 const int MAXN = 25;
14 const int INF = 0x3f3f3f3f;
15 int a[MAXN];
16 bool vis[MAXN];
17 int n, ans;
18
19 void DFS(int sum, int tot)
20 {
21 if (tot >= ans) return ;
22 if (sum == 0) {ans = min (ans, tot); return ;}
23
24 for (int i=1; i<=n; ++i)
25 {
26 if (!vis[i])
27 {
28 vis[i] = true;
29 int s1 = (i == 1) ? n : i - 1;
30 int s2 = (i == n) ? 1 : i + 1;
31 if (vis[s1]) s1 = 24;
32 if (vis[s2]) s2 = 24;
33 vis[s1] = true; vis[s2] = true;
34 sum -= a[s1]; sum -= a[s2]; sum -= a[i];
35
36 tot += sum;
37 DFS (sum, tot);
38 tot -= sum;
39
40 sum += a[s1]; sum += a[s2]; sum += a[i];
41 vis[s1] = false; vis[s2] = false; vis[i] = false;
42 }
43 }
44 }
45
46 int main(void) //URAL 1152 False Mirrors
47 {
48 //freopen ("N.in", "r", stdin);
49
50 while (scanf ("%d", &n) == 1)
51 {
52 int sum = 0; a[24] = 0;
53 for (int i=1; i<=n; ++i) {scanf ("%d", &a[i]); sum += a[i];}
54 memset (vis, false, sizeof (vis));
55
56 ans = INF; DFS (sum, 0);
57 printf ("%d
", ans);
58 }
59
60 return 0;
61 }