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C/nqueens.cpp

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+
+#include<stdio.h>
+#include<math.h>
+ void queen(int row,int n);
+int board[20],count;
+
+int main()
+{
+int n,i,j;
+
+
+printf(" - N Queens Problem Using Backtracking -");
+printf("\n\nEnter number of Queens:");
+scanf("%d",&n);
+queen(1,n);
+return 0;
+}
+
+//function for printing the solution
+void print(int n)
+{
+int i,j;
+printf("\n\nSolution %d:\n\n",++count);
+
+for(i=1;i<=n;++i)
+  printf("\t%d",i);
+
+for(i=1;i<=n;++i)
+{
+  printf("\n\n%d",i);
+  for(j=1;j<=n;++j) //for nxn board
+  {
+   if(board[i]==j)
+    printf("\tQ"); //queen at i,j position
+   else
+    printf("\t-"); //empty slot
+  }
+}
+}
+
+/*funtion to check conflicts
+If no conflict for desired postion returns 1 otherwise returns 0*/
+int place(int row,int column)
+{
+int i;
+for(i=1;i<=row-1;++i)
+{
+  //checking column and digonal conflicts
+  if(board[i]==column)
+   return 0;
+  else
+   if(abs(board[i]-column)==abs(i-row))
+    return 0;
+}
+
+return 1; //no conflicts
+}
+
+//function to check for proper positioning of queen
+void queen(int row,int n)
+{
+int column;
+for(column=1;column<=n;++column)
+{
+  if(place(row,column))
+  {
+   board[row]=column; //no conflicts so place queen
+   if(row==n) //dead end
+    print(n); //printing the board configuration
+   else //try queen with next position
+    queen(row+1,n);
+  }
+}
+}