1 #include <stdio.h>
2 #include <stdlib.h>
3
4 /* this code is used to cope with the problem of the eight queens.
5 * array borad[9][9] is a virtual borad.
6 * line 0 and volumn 0 is ignored.
7 * at first we find a place to set a queen on it, then mark this queen's
8 * domain. the way of marking domain is add 1 on the board[line][volumn],
9 * so the number of board[line][volumn] means this place can attacked by
10 * how many queens. after we mark this queen's domain, we move on to next line.
11 * if there is no next line, we got a solution */
12 /* 这些代码主要用来解决八皇后问题
13 * 数组borad[9][9]是一个虚拟的棋盘。
14 * 第0行跟第0列被忽略
15 * 在最开始时，我们在某一行上找到一个位置，放上皇后后，我们把这个皇后能
16 * 攻击的范围都标志起来。我们标志的方法是在board[行][列]上加1，
17 * 所以board[行][列]上的值意味着这个位置能被多少个皇后攻击
18 * 当我们标志好这个皇后的范围后，我们就跳到下一行去。
19 * 如果已经没有下一行了，那么我们就找到一个放置方法了 */
20
21 /* if a place on board have been marked by NONE
22 * it means no queen can attack this place, it is a potential place to set a queen */
23 /* 如果棋盘上一个位置被设置为NONE，意味着没有皇后能攻击这个位置，这个位置可以被设置为皇后 */
24 #define NONE (0)
25 #define QUEEN (-1)
26
27 #define OCCUPY (1)
28 #define DISOCCUPY (0)
29
30 void Compute(int line) ;
31 void PrintBorad(void) ;
32 void operate_borad(int line, int volumn, int function) ;
33
34 int main(void)
35 {
36 Compute(1) ;
37 return 0 ;
38 }
39
40 /* ignored the first line and the first volumn */
41 int borad[9][9] ;
42
43 /* this is a recursive function.
44 * it will find a queen on this line,
45 * then fine next one of next line by call itself */
46 /* 这是一个递归函数。在某一行上找到皇后的位置，然后调用自己找下一行的皇后 */
47 void Compute(int line)
48 {
49 int i ;
50 static int num_of_solution = 0;
51
52 for(i = 1; i <= 8; i++)
53 if(borad[line][i] == NONE)
54 {
55 operate_borad(line, i, OCCUPY) ;
56 if(line == 8) // find a solution
57 {
58 printf("%d\n", ++num_of_solution) ;
59 PrintBorad() ;
60 }
61 else Compute(line +1) ; /* contine to next line */ /* 查找一行的皇后 */
62 operate_borad(line, i, DISOCCUPY) ;
63 }
64 }
65
66 /* function:
67 * if function is OCCUPY, then set a flag of queen on borad[line][volumn]
68 * and set a flag on the domain of this queen
69 * if function is DISOCCUPY, then clear flag of queen on borad[line][volumn]
70 * and clear the flag on the domain of this queen */
71 /* 功能：
72 * 如果function变量是OCCUPY，那么在board[line][volumn]上放上皇后，
73 * 并设置这个皇后的攻击范围
74 * 如果function变量是DISOCCUPY,那么把皇后从board[line][volumn]上清除
75 * 并清除这个皇后在其攻击范围上所设置的标志 */
76 void operate_borad(int line, int volumn, int function)
77 {
78 int i, j, *temp, nl, nv ;
79
80 borad[line][volumn] = (function == OCCUPY ? QUEEN : NONE) ;
81
82 /* i and j are used to decide the direction*/
83 for(i = -1; i <= 1; i++)
84 for(j = -1; j <= 1; j++)
85 if(i == 0 && j == 0) continue ;
86 else
87 for(nl = line +i, nv = volumn +j ;
88 nl >= 1 && nl <= 8 && nv >= 1 && nv <= 8 ;
89 nl += i, nv += j)
90 {
91 temp = &borad[nl][nv] ;
92 /* add one means this place can be attack by another queen */
93 function == OCCUPY ? (*temp)++ : (*temp)-- ;
94 }
95 }
96 /* function: print the board on the screen */
97 /* 打印棋盘 */
98 void PrintBorad(void)
99 {
100 int x, y, chess ;
101
102 for(x = 1; x <= 8; x++)
103 {
104 for(y = 1; y <= 8; y++)
105 {
106 chess = borad[x][y] ;
107 if(chess != QUEEN)
108 putchar('*') ;
109 else
110 putchar('Q') ;
111 }
112 putchar('\n') ;
113 }
114 }
