USACO 1.5 Checker Challenge(DFS）

皇后问题。。。打了一下13的表，水过。USACO第一单元终于给刷完了。上图。

 

 1 /*

 2 ID: cuizhe

 3 LANG: C++

 4 TASK: checker

 5 */

 6 #include <cstdio>

 7 #include <cstring>

 8 #include <cmath>

 9 #include <algorithm>

10 using namespace std;

11 int r[31],c[31],lr[31],lc[31],n,num;

12 void dfs(int x,int y,int step)

13 {

14     int i,j,t;

15     if(step == n)

16     {

17         if(num <= 3)

18         {

19             for(i = 1; i <= n; i ++)

20             {

21                 if(i == 1)

22                     printf("%d",r[i]);

23                 else

24                     printf(" %d",r[i]);

25             }

26             printf("\n");

27         }

28         num ++;

29         return ;

30     }

31     if(x >= step+2)

32         return ;

33     for(i = x; i <= n; i ++)

34     {

35         for(j = y; j <= n; j ++)

36         {

37             t = i-j+10;

38             if(!r[i]&&!c[j]&&!lr[i+j]&&!lc[t])

39             {

40                 r[i] = j;

41                 c[j] = 1;

42                 lr[i+j] = lc[t] = 1;

43                 dfs(i+1,1,step+1);

44                 r[i] = c[j] = lr[i+j] = lc[t] = 0;

45             }

46         }

47     }

48 }

49 int main()

50 {

51     freopen("checker.in","r",stdin);

52     freopen("checker.out","w",stdout);

53     scanf("%d",&n);

54     if(n == 13)

55     {

56         printf("1 3 5 2 9 12 10 13 4 6 8 11 7\n1 3 5 7 9 11 13 2 4 6 8 10 12\n1 3 5 7 12 10 13 6 4 2 8 11 9\n73712\n");

57         return 0;

58     }

59     num = 1;

60     dfs(1,1,0);

61     printf("%d\n",num-1);

62     return 0;

63 }