add an 8-queue solution

Author: xtaci

Makefile

@@ -66,7 +66,8 @@ PROGRAMS =  m_based_demo \
 			scc_demo \
 			sort_demo \
 			bubble_sort_demo \
-			selection_sort_demo
+			selection_sort_demo	\
+			8queue_demo
 
 all: $(PROGRAMS)
 

README.md

@@ -88,6 +88,7 @@
     K-Means
     Knuth–Morris–Pratt algorithm
     Disjoint-Set
+	8-Queue Problem
 
 ####贡献者 ( Contributors ) :  
     Samana :  for heavy work of MSVC compatability

include/8queen.h

@@ -0,0 +1,87 @@
+/*******************************************************************************
+ * DANIEL'1'S ALGORITHM IMPLEMENTAIONS
+ *
+ *  /\  |  _   _  ._ o _|_ |_  ._ _   _ 
+ * /--\ | (_| (_) |  |  |_ | | | | | _> 
+ *         _|                      
+ * 8-Queue 
+ *
+ * http://en.wikipedia.org/wiki/Eight_queens_puzzle
+ ******************************************************************************/
+
+#ifndef __8QUEEN_H__
+#define __8QUEEN_H__
+
+#include <stdio.h>
+#include <string.h>
+
+namespace alg {
+	class Queen8 {
+		private:
+			char board[8][8];
+			int cnt;
+		public:
+			void solve() {
+				memset(board, '0', sizeof(board));
+				cnt = 0;
+				_solve(0);
+			}
+		private:
+			void _solve(int row) {	// start from 0
+				int i;
+				for (i=0;i<8;i++) {
+					board[row][i] = '1';
+					if (check(row, i)) {
+						if (row == 7) print();
+						else _solve(row+1);
+					}
+					board[row][i] = '0';	// rollback
+				}
+			}
+
+			void print() {
+				printf("chessboard: %d\n",++cnt);
+				int i,j;
+				for (i=0;i<8;i++) {
+					for (j=0;j<8;j++) {
+						printf("%c ", board[i][j]);
+					}
+					printf("\n");
+				}
+			}
+
+			bool check(int row, int col) {
+				int i,j;
+
+				// cannot be same column
+				for (i=0;i<row;i++) {
+					if (board[i][col] == '1') {
+						return false;
+					}
+				}
+
+				// cannot be diagnal
+				i = row-1, j = col-1;
+				while (i>=0 && j >=0) {
+					if (board[i][j] == '1') {
+						return false;
+					}
+					i--;
+					j--;
+				}
+
+				i = row-1, j = col+1;
+				while (i>=0 && j <8) {
+					if (board[i][j] == '1') {
+						return false;
+					}
+					i--;
+					j++;
+				}
+
+				return true;
+			}
+	};
+}
+
+#endif //__8QUEEN_H__

src/8queue_demo.cpp

@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include <8queen.h>
+
+int main(void) {
+	alg::Queen8 q;
+	q.solve();
+}
+