A crude version to solve the n-queens problem (wasn't as hard as I expected):
import java.lang.*;
class NQueens {
int N;
int[][] Board;
int soln=0;
public static void main(String[] args) {
int N=Integer.parseInt(args[0]);
NQueens nq = new NQueens(N);
System.out.println("Solving the "+N+"-queen problem.");
nq.search(0);
}
NQueens(int n) {
N=n;
Board = new int[N][N];
}
boolean IsValid() {
int tot=0;
int col=0;
int row=0;
// Check column totals first
for(col=0;col
tot=0;
for(row=0;row
tot+=Board[row][col];
if(tot>1)
return false;
}
// Check diagonals slanting right
for(col=0;col
tot=0;
for(row=0;row<=col;row++) {
tot+=Board[row][col-row];
}
if(tot>1)
return false;
}
for(col=1;col
tot=0;
for(row=N-1;row>=col;row--) {
tot+=Board[row][col+N-1-row];
}
if(tot>1)
return false;
}
//Check diagonals slanting left
for(col=N-1;col>=0;col--) {
tot=0;
for(row=0;row<=(N-1-col);row++) {
tot+=Board[row][col+row];
}
if(tot>1)
return false;
}
//Check diagonals slanting left
for(row=N-1;row>0;row--) {
tot=0;
for(col=0;col<=(N-1-row);col++) {
tot+=Board[row+col][col];
}
if(tot>1)
return false;
}
return true;
}
void search(int row) {
if (row==N) {
// We have found a solution!
soln++;
System.out.println("Solution "+soln);
printBoard();
return;
}
for(int col=0;col
Board[row][col]=1;
if(IsValid()) {
search(row+1);
}
Board[row][col]=0;
}
}
void printBoard() {
for(int row=0;row
for(int col=0;col
if(Board[row][col]==1)
System.out.print(" Q ");
else
System.out.print(" X ");
}
System.out.println("");
}
}
}
