DFS水题 URAL 1152 False Mirrors

 

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\n", ans);
58     }
59 
60     return 0;
61 }

 

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