USACO 5.2 Snail Trails(DFS)

DFS，1Y啊。。

 1 /*

 2 ID: cuizhe

 3 LANG: C++

 4 TASK: snail

 5 */

 6 #include <iostream>

 7 #include <cstdio>

 8 #include <cstring>

 9 #include <queue>

10 #include <map>

11 #include <cmath>

12 #include <algorithm>

13 using namespace std;

14 int a[4] = {0,1,-1,0};

15 int b[4] = {1,0,0,-1};

16 int o[201][201];

17 int n,ans;

18 void dfs(int x,int y,int pos,int step)

19 {

20     int i;

21     ans = max(step,ans);

22     if(x+a[pos] <= n&&x+a[pos] >= 1&&y+b[pos] >= 1&&y+b[pos] <= n&&!o[x+a[pos]][y+b[pos]])

23     {

24         o[x+a[pos]][y+b[pos]] = 2;

25         dfs(x+a[pos],y+b[pos],pos,step+1);

26         o[x+a[pos]][y+b[pos]] = 0;

27     }

28     else  if(x+a[pos] <= n&&x+a[pos] >= 1&&y+b[pos] >= 1&&y+b[pos] <= n&&o[x+a[pos]][y+b[pos]] == 2)

29     {

30         return ;

31     }

32     else

33     {

34         for(i = 0; i < 4; i ++)

35         {

36             if(pos == 0||pos == 3)

37             {

38                 if(i == 1||i == 2)

39                 {

40                     if(x+a[i] <= n&&x+a[i] >= 1&&y+b[i] >= 1&&y+b[i] <= n&&!o[x+a[i]][y+b[i]])

41                     {

42                         o[x+a[i]][y+b[i]] = 2;

43                         dfs(x+a[i],y+b[i],i,step+1);

44                         o[x+a[i]][y+b[i]] = 0;

45                     }

46                 }

47             }

48             else

49             {

50                 if(i == 0||i == 3)

51                 {

52                     if(x+a[i] <= n&&x+a[i] >= 1&&y+b[i] >= 1&&y+b[i] <= n&&!o[x+a[i]][y+b[i]])

53                     {

54                         o[x+a[i]][y+b[i]] = 2;

55                         dfs(x+a[i],y+b[i],i,step+1);

56                         o[x+a[i]][y+b[i]] = 0;

57                     }

58                 }

59             }

60         }

61     }

62     return ;

63 }

64 int main()

65 {

66     int m,i,j,len,sv,ev;

67     char ch[101];

68     freopen("snail.in","r",stdin);

69     freopen("snail.out","w",stdout);

70     scanf("%d%d",&n,&m);

71     for(i = 0; i < m; i ++)

72     {

73         scanf("%s",ch);

74         len = strlen(ch);

75         sv = ch[0]-'A' + 1;

76         ev = 0;

77         for(j = 1; j < len; j ++)

78         {

79             ev = ev*10 + ch[j]- '0';

80         }

81         o[sv][ev] = 1;

82     }

83     o[1][1] = 2;

84     dfs(1,1,0,1);

85     dfs(1,1,1,1);

86     printf("%d\n",ans);

87     return 0;

88 }