lab12

 #include<stdio.h> 

#include<math.h> 

#include<stdlib.h> 

int board[20],count; 

int main() 

{ 

int n,i,j; 

void queen(int row,int n); 

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) 

{ 

39 

Department of CSE (CY), RNSIT         

IV Semester          

BCSL404 – ADA LABORATORY 

//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); 

} 

} 

}