[JAVA] n-queen

class Solution {
    int N;
    int[] board;
    int answer;
    public int solution(int n) {
        board=new int[n+2];
        N=n;
        answer=0;
        dfs(1);
        return answer;
    }
    public Boolean isPromising(int pos){
        
        for(int i=1;i<pos;i++){
            if((pos-i)==Math.abs(board[pos]-board[i])
               || (board[pos]==board[i])
              ){
                return false;
            }
            
            
        }
        return true;
    }
    public void dfs(int pos){
        if(isPromising(pos-1)){
            if(pos==N+1){
                answer++;
                return;
            }
            if(pos>N+1)
                return;
            
            for(int i=1;i<=N;i++){
                board[pos]=i;
                dfs(pos+1);
            }
        }
    }
}