1 //经典的N皇后问题
 2 #include <iostream>
 3 #include <stdio.h>
 4 #include <memory.h>
 5 using namespace std;
 6 
 7 int ch[25][25];
 8 int n, num, result[25];
 9 
10 void dfs(int x, int y)
11 {
12     if(ch[x][y]) return;    //如果该点已经被攻击，则返回
13     int i, xx, yy;
14     if(x == n)  //如果
15     {
16         num++;
17         return;
18     }
19 
20     //下面个人觉得比较巧妙，因为会有重复的地方很难分析是属于哪个皇后
21     //若用了下面位置的 ++ or -- ，则巧妙地避免上述情况
22     //一共八个方向进行标记：上、下、左、右、左上、左下、右上、右下
23     xx = x; yy = y;
24     while(xx>0)  ch[xx--][y]++;
25     xx = x; yy = y;
26     while(yy>0)  ch[x][yy--]++;
27     xx = x; yy = y;
28     while(xx<=n) ch[xx++][y]++;
29     xx = x; yy = y;
30     while(yy<=n) ch[x][yy++]++;
31     xx = x; yy = y;
32     while(xx<=n && yy<=n) ch[xx++][yy++]++;
33     xx = x; yy = y;
34     while(xx>0  && yy<=n) ch[xx--][yy++]++;
35     xx = x; yy = y;
36     while(xx<=n && yy>0)  ch[xx++][yy--]++;
37     xx = x; yy = y;
38     while(xx>0  && yy>0)  ch[xx--][yy--]++;
39 
40     for(i = 1; i <= n; i++)
41     {
42         dfs(x+1, i);
43     }
44 
45     //若这个皇后深搜后的结果不成功，则要返回原来的情况，八个方向都 --
46     xx = x; yy = y;
47     while(xx>0)  ch[xx--][y]--;
48     xx = x; yy = y;
49     while(yy>0)  ch[x][yy--]--;
50     xx = x; yy = y;
51     while(xx<=n) ch[xx++][y]--;
52     xx = x; yy = y;
53     while(yy<=n) ch[x][yy++]--;
54     xx = x; yy = y;
55     while(xx<=n && yy<=n) ch[xx++][yy++]--;
56     xx = x; yy = y;
57     while(xx>0  && yy<=n) ch[xx--][yy++]--;
58     xx = x; yy = y;
59     while(xx<=n && yy>0)  ch[xx++][yy--]--;
60     xx = x; yy = y;
61     while(xx>0  && yy>0)  ch[xx--][yy--]--;
62 }
63 
64 void init()     //初始化函数
65 {
66     int i, j;
67     for(i = 0; i < 12; i++)
68         for(j = 0; j < 12; j++)
69             ch[i][j] = 0;
70 }
71 
72 void set()
73 {
74     int i, k;
75     for(k = 1; k <= 10; k++)
76     {
77         num = 0; n = k;     //初始化
78         for(i = 1; i <= k; i++)
79         {
80             init();         //初始化
81             dfs(1, i);      //继续dfs寻找
82         }
83         result[k] = num;
84     }
85 }
86 
87 int main()
88 {
89     set();
90     while(scanf("%d", &n), n)
91     {
92         printf("%d\n", result[n]);
93     }
94 
95     return 0;
96 }