USACO 4.4 Shuttle Puzzle(dfs)

比较有意思的一个题，虽然不知道为什么这么做。。。看样例就可以发现一般是w_  _b  wb_ _bw只能这样4种操作。。。没想到就这样过了。。注意了一下20个换行，2Y。。。我开始还在想bfs还想过，直接构造，构造不出来。。。

  1 /*
  2 ID:cuizhe
  3 LANG: C++
  4 TASK: shuttle
  5 */
  6 #include <iostream>
  7 #include <cstdio>
  8 #include <map>
  9 #include <algorithm>
 10 #include <cstring>
 11 #include <string>
 12 using namespace std;
 13 map<string,int> mp;
 14 char str[32];
 15 int que[100001];
 16 int a[100001];
 17 int ans = 10000000;
 18 int n;
 19 int judge()
 20 {
 21     int i;
 22     for(i = 0; i < n; i ++)
 23         if(str[i] != '2')
 24             break;
 25     if(i == n&&str[n] == ' ')
 26         return 1;
 27     else
 28         return 0;
 29 }
 30 void dfs(int x,int step)
 31 {
 32     int i;
 33     if(ans <= step) return;
 34     if(judge())
 35     {
 36         if(step-1 < ans)
 37         {
 38             ans = step-1;
 39             for(i = 1;i <= ans;i ++)
 40             a[i] = que[i];
 41         }
 42         return ;
 43     }
 44     if(x-1 >= 0&&x-2 >= 0&&str[x-1] == '2'&&str[x-2] == '1')
 45     {
 46         que[step] = x-2;
 47         str[x-2] = ' ';
 48         str[x] = '1';
 49         dfs(x-2,step+1);
 50         str[x-2] = '1';
 51         str[x] = ' ';
 52     }
 53     if(x-1 >= 0&&str[x-1] == '1')
 54     {
 55         que[step] = x-1;
 56         str[x] = '1';
 57         str[x-1] = ' ';
 58         dfs(x-1,step+1);
 59         str[x] = ' ';
 60         str[x-1] = '1';
 61     }
 62     if(x+1 <= 2*n&&x+2 <= 2*n&&str[x+1] == '1'&&str[x+2] == '2')
 63     {
 64         que[step] = x+2;
 65         str[x+2] = ' ';
 66         str[x] = '2';
 67         dfs(x+2,step+1);
 68         str[x+2] = '2';
 69         str[x] = ' ';
 70     }
 71     if(x+1 <= 2*n&&str[x+1] == '2')
 72     {
 73         que[step] = x+1;
 74         str[x] = '2';
 75         str[x+1] = ' ';
 76         dfs(x+1,step+1);
 77         str[x] = ' ';
 78         str[x+1] = '2';
 79     }
 80     return ;
 81 }
 82 int main()
 83 {
 84     int i;
 85     freopen("shuttle.in","r",stdin);
 86     freopen("shuttle.out","w",stdout);
 87     scanf("%d",&n);
 88     for(i = 0; i < n; i ++)
 89     {
 90         str[i] = '1';
 91         str[n+i+1] = '2';
 92     }
 93     str[n] = ' ';
 94     dfs(n,1);
 95     for(i = 1;i <= ans;i ++)
 96     {
 97         if(i%20 == 0||i == ans)
 98         printf("%d\n",a[i]+1);
 99         else
100         printf("%d ",a[i]+1);
101     }
102     return 0;
103 }

 

posted @ 2013-03-29 14:29  Naix_x  阅读(166)  评论(0)  编辑  收藏  举报